Toothbrush employing acoustic waveguide

ABSTRACT

A power toothbrush ( 10 ) is disclosed having a handle ( 15 ), battery ( 12 ), ultrasonic drive circuit ( 14 ), motor ( 16 ), control unit ( 18 ), and toothbrush head ( 20 ). The toothbrush head includes bristles ( 26 ) and a waveguide ( 24 ) that is operatively connected to an ultrasonic transducer ( 22 ). The waveguide facilitates the transmission of acoustic energy into the dental fluid to achieve improved cleaning and stain removal and improved cleaning in interproximal and subgingival regions. In one embodiment an ultrasound transducer module ( 30 ) includes a plurality of piezoelectric elements ( 32, 34 ) that may be mechanically connected in series, and electrically connected in parallel. One or more contacts ( 36 ) connect the elements, and a waveguide structure ( 50 ). An impedance matching layer ( 38 ) may be provided between the waveguide and the ultrasonic transducer module. The waveguide may be formed from an relatively soft material, for example, a polymer having a hardness between 10 and 65 Shore A.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/981,735, filed Nov. 3, 2004, which claims the benefit ofU.S. Provisional Application No. 60/517,638, filed on Nov. 4, 2003. Thisapplication also claims the benefit of U.S. Provisional Application No.60/677,577, filed May 3, 2005. The disclosures of the priority patentapplications are expressly incorporated herein by reference in theirentireties.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

One or more of the inventions disclosed herein were made with Governmentsupport under SBIR Contract No. 1-R43-DEO16761-01. The Government mayhave certain rights in one or more of those inventions.

BACKGROUND

Existing power toothbrushes, even the most effective, leave clinicallysignificant plaque at tooth contact surfaces, at the gingival-toothcontact points, below the gingiva, and beyond the direct reach of thebristles or other toothbrush components. Previous attempts at creatingultrasonic toothbrushes failed to exploit microbubble formation indental fluid for purposes of facilitating plaque removal or failed toconsider microbubbles and macrobubbles as a potential impediment toultrasound propagation beyond the bristle tips. Some early toothbrushesthat employed ultrasound technology attempted propagation of ultrasoundwaves from the base of the bristles either through the bristlesthemselves or through the bubbly dental fluid that fills the spacesbetween the bristles. See, e.g., U.S. Pat. No. 5,138,733, No. 5,247,716,No. 5,369,831, and No. 5,546,624, to Bock. Because conventionaltoothbrush bristles and bubbly dental fluid can reduce rather thanfacilitate the propagation of ultrasound waves, those toothbrushes fellshort of achieving efficient ultrasound wave propagation. Also, theultrasound systems in prior art toothbrushes did not take advantage ofthe specific bubbly structure within dental fluid.

SYNOPSIS OF THE ART

U.S. Pat. No. 3,335,443, to Parisi, discloses a brush that is coupled toan ultrasonic, vibratory, handheld dental instrument that is capable ofbeing vibrated at high sonic and ultrasonic frequencies.

U.S. Pat. No.3,809,977, to Balamuth et al., which reissued as U.S. Pat.No. 28,752, discloses ultrasonic kits, ultrasonic motor constructions,and ultrasonic converter designs for use alone or in combination. Theultrasonic motor may be of piezoelectric material having a removable tipand is contained in a housing having an electrical contact means adaptedto be plugged into an adapter that is connected to a converter.

U.S. Pat. No. 3,828,770, to Kuris et al., discloses a method forcleaning teeth employing bursts of ultrasonic mechanical vibration at anapplicator repeated at a sonic frequency to produce both ultrasonic andsonic vibratory motion during use.

U.S. Pat. No. 3,840,932 and No. 3,941,424, to Balamuth et al., disclosean ultrasonic toothbrush applicator in a configuration to beultrasonically vibrated to transmit mechanical vibrations from one endto a bristle element positioned at the other end.

U.S. Pat. No. 4,071,956, to Andress, discloses a device, that is not atoothbrush, for removing dental plaque by ultrasonic vibrations.

U.S. Pat. No. 4,192,035, to Kuris, discloses an apparatus comprising anelongated member formed of a piezoelectric member with a pair ofcontacting surfaces with a brush member adapted to be received withinthe human mouth. A casing adapted into a handle is configured to receivethe piezoelectric member.

U.S. Pat. No. 4,333,197, to Kuris, discloses an ultrasonic toothbrushthat includes an elongated handle member in the form of a hollow housinghaving disposed therein a low voltage coil and cooperating ferrite corethat is driven at ultrasonic frequencies. A brush member is affixed tothe core and is adhesively affixed to an impedance transfer device thatis adhesively affixed to the core material. The impedance transferdevice insures maximum transfer of ultrasonic energy from the corematerial to the brush.

U.S. Pat. No. 4,991,249 and No. 5,150,492, to Suroff, disclose anultrasonic toothbrush having an exchangeable toothbrush member that isremovably attached to an ultrasonic power member.

U.S. Pat. No. 5,138,733, to Bock, discloses an ultrasonic toothbrushhaving a handle, a battery pack, an electronics driving module, apiezoelectric member, and a removable brush head. The piezoelectriccrystal resonates, expands and contracts volumetrically, in tune withthe frequency supplied by the electronic driving modules, therebyconverting electronic energy into sound-wave energy.

U.S. Pat. No. 5,247,716, to Bock, discloses a removable brush head foran ultrasonic toothbrush having a plurality of bristle clusters, asubstantially tubular body constructed of a flexible material, andtensioning means securing the brush head to the ultrasonic device,providing for the efficient transmission of ultrasonic frequencyvibrations from the device via the brush head.

U.S. Pat. No. 5,311,632, to Center, discloses a device for removingplaque from teeth comprising a toothbrush having a thick, cylindrical,hollow handle encompassing (1) an electric motor that is actuable tocause rotation of an eccentrically mounted member and vibration of theentire device, and (2) an ultrasonic transducer actuable to produce highfrequency sound waves along the brush.

U.S. Pat. No. 5,369,831, to Bock, discloses a removable brush head foran ultrasonic toothbrush.

U.S. Pat. No. 5,546,624, to Bock, discloses an ultrasonic toothbrushincluding a handle constructed of a rigid material, a battery pack, anelectronics driving module, a piezoelectric member, and a removablebrush head. The piezoelectric crystal resonates, expands and contractsvolumetrically, in tune with the frequency supplied by the electronicdriving module and thereby converts the electronic energy intosound-wave energy.

Japanese Application No. P1996-358359, Patent Laid Open 1998-165228,discloses a toothbrush utilizing ultrasonic waves in which an ultrasonicwave generator is provided in the handle of a manual or electricallypowered toothbrush and an ultrasonic wave vibrator is mounted in thebrush and wired to the wave generator.

Japanese Application No. P2002-353110, Patent Laid Open 2004-148079,discloses an ultrasonic toothbrush wherein ultrasonic vibration isradiated from a piezoelectric vibrator arranged inside a brush head andtransmitted to the teeth via a rubber projection group.

U.S. Pat. No. 6,203,320, to Williams et al., discloses an electricallyoperated toothbrush and method for cleaning teeth. The toothbrushincludes a handle, a brush head connected to the handle having aplurality of hollow filament bristles, passageways through the handleand brush head for transporting fluid into and through the hollowfilament bristles, an electrical energy source in the handle, and avibratory element for imparting a pulsation to the fluid beingtransported.

U.S. Patent Publication No. 2003/0079305, to Takahata et al., disclosesan electric toothbrush in which a brush body is simultaneouslyoscillated and reciprocated. The electric toothbrush comprises a casingmain body, an arm extending above the casing main body, a brush bodyarranged in a top end of the arm, and an ultrasonic motor arranged in atop end inside of the arm for driving the brush body.

U.S. Pat. No. 35,712, which is a reissue of U.S. Pat. No. 5,343,883, toMurayama, discloses an electric device (i.e., a flosser) for removal ofplaque from interproximal surfaces. The device employs sonic energy anddental floss secured between two tines of a flexible fork removablyattached to a powered handle. The electric motor revolves at sonicfrequencies to generate sonic energy that is transmitted to the flexiblefork.

U.S. Pat. No. 6,619,957, to Mosch et al., discloses an ultrasonic scalercomprising a scaler tip, actuator material, a coil, a handpiece housing,and an air-driven electrical current generator. The actuator material,coil, and air-driven electrical current generator are all encompassedwithin the handpiece housing.

U.S. Pat. No. 6,190,167, to Sharp, discloses an ultrasonic dental scalerfor use with a dental scaler insert having a resonant frequency. Thedental scaler insert is removably attached to a handpiece having anenergizing coil coupled to a selectively tunable oscillator circuit togenerate a control signal having an oscillation frequency for vibratingthe dental scaler.

U.S. Pat. No. 4,731,019, to Martin, discloses a dental instrument forscaling by ultrasonic operation. The instrument of the dental instrumenthas a distal end with a hook-like configuration with a conical pointedend and comprising abrasive particles, typically diamond particles.

U.S. Pat. No. 5,150,492, to Suroff, discloses an ultrasonic toothbrushhaving an exchangeable ultrasonic implement that may be removablymounted to an ultrasonic power means that is encompassed within thetoothbrush handle.

U.S. Pat. No. 5,378,153, to Giuliani, discloses a dental hygieneapparatus having a body portion and an extended resonator arm. Theapparatus employs an electromagnet in its body that acts in combinationwith two permanent magnets to achieve an oscillating action about atorsion pin. The arm is driven such that the bristle-tips operate withinranges of amplitude and frequency to produce a bristle tip velocitygreater than 1.5 meters per second to achieve cleansing beyond the tipsof the bristles.

There remains a need in the art for toothbrush designs that achieveimproved dental cleaning properties between the teeth and gums, atpoints of contact between the teeth, and beyond the direct action of thebristles.

SUMMARY

The present invention fulfills these and other related needs byproviding toothbrushes, including power and manual toothbrushes, thatemploy an acoustic waveguide, either alone or in combination with anultrasonic transducer and/or sonic component, to achieve improved plaqueand stain removal and user experience. Accordingly, within certainembodiments, the present invention provides power toothbrushes havingone or more acoustic waveguide(s) that is capable of propagating and mayfunction to focus acoustic waves transmitted by an ultrasonic transducerinto the dental fluid, thereby inducing cavitation of microbubbles and,in addition or alternately, inducing acoustic streaming, with aconsequent improvement in the loosening and removal of dental plaquefrom dental surfaces and interproximal regions. When used in combinationwith a sonic component, the acoustic waveguide can, additionally oralternatively, be made to vibrate such that the acoustic waveguidecontributes to enhanced fluid flow in the oral cavity and to theformation of microbubbles in the dental fluid, beyond the reach of theacoustic waveguide and/or toothbrush head bristle tips. When used incombination with a sonic component, the enhanced bubbly fluid flowgenerated by the acoustic waveguide can, additionally or alternatively,work synergistically with the ultrasound transmitted through theacoustic waveguide to further facilitate plaque and stain removal beyondthe reach of the acoustic waveguide and/or toothbrush head bristle tips.

In an embodiment of the present invention, an ultrasonic transducer isutilized at the toothbrush head, at the base of and in operableproximity to an acoustic waveguide or, alternatively, mechanicallycoupled to the toothbrush head from within the toothbrush handle via anacoustically transmitting conduit (made, for example, from metal, gel,or fluid). In either embodiment, the ultrasonic transducer transmitsultrasonic waves to the acoustic waveguide that, in turn, propagatesthose ultrasonic waves into the dental fluid such that the waves areeffective in causing cavitation of microbubbles within the dental fluidand, alternatively or additionally, acoustic streaming. Within certainembodiments, toothbrushes of the present invention may also comprise oneor more toothbrush bristle tufts that contribute to the generation ofmicrobubbles within the dental fluid. The ultrasonic waves causecavitation of those microbubbles that, in turn, results in the improvedplaque and stain removal properties of toothbrushes disclosed herein.

Additional embodiments of the present invention provide powertoothbrushes having an ultrasonic transducer and an acoustic waveguidein further combination with a sonic component that operates within theaudible frequencies to mechanically move the brush head, including thebristles and acoustic waveguide, to increase flow of the dental fluid ata velocity and intensity required to contribute to microbubbleproduction. The acoustic waveguide and ultrasonic waves that ittransmits act in a synergistic fashion to produce a scrubbing bubbly jetwithin the dental fluid, both by increasing the instantaneous spatialdistribution of bubbles available for activation, and by increasing thedistribution of ultrasound owing to the sonic motion of the acousticwaveguide. The acoustic waveguide and ultrasonic waves also actsynergistically to create a bubbly jet by each contributing to theacceleration of the bubbly fluid, the acoustic waveguide by pushingfluid directly and the ultrasonic waves by inducing acoustic streaming.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1A is a schematic, partially cross-sectional diagram depicting anexemplary power toothbrush of the present invention;

FIG. 1B is a perspective view of one embodiment of an ultrasonictransducer module of the present invention;

FIG. 1C is a perspective, partially broken-away view of one embodimentof an acoustic waveguide in combination with the ultrasonic transducermodule shown in FIG. 1B;

FIG. 2A is a diagram depicting a cross-sectional view of an exemplarypower toothbrush head similar to the embodiment illustrated in FIG. 1A,showing a handle, bristles, an ultrasonic transducer, and an acousticwaveguide shaped generally as a rectangular solid with a convex tip;

FIG. 2B is a diagram depicting a finite element model simulationgeometry of the exemplary toothbrush head shown in FIG. 2A (shown herewithout bristles);

FIG. 2C is a diagram depicting the simulated ultrasound wave field at1.2 ms post-pulse wherein the ultrasonic waves remain mainly in theacoustic waveguide;

FIG. 2D is a diagram depicting the simulated ultrasound wave field at2.0 ms post-pulse, wherein the ultrasonic waves have substantially leftthe acoustic waveguide;

FIG. 3A is a diagram depicting a finite element model simulationgeometry of a toothbrush head wherein the exemplary acoustic waveguidehas a tapered profile;

FIG. 3B is a perspective view of the tapered profile waveguide shown inFIG. 3A;

FIG. 3C is a side view of the simulated wave field plot soon afterultrasonic transmission, showing propagation within the acousticwaveguide;

FIG. 3D is a side view of the simulated wave field plot at a later timesubsequent to ultrasonic transmission showing acoustic waveguidepropagation of the ultrasonic wave front into the fluid emulsion;

FIG. 3E is an end view of the simulated wave field plot at the samesimulation time as FIG. 3C;

FIG. 3F is an end view of the simulated wave field plot at the samesimulation time as FIG. 3D;

FIG. 4A is a finite element model simulation geometry of anotherexemplary acoustic waveguide, wherein the waveguide tip is curved;

FIG. 4B is a perspective view of the waveguide shown in FIG. 4A, whereinthe portion beyond the curved dotted line is removed;

FIG. 4C is the simulated wave field plot soon after ultrasonictransmission, showing propagation within the acoustic waveguide;

FIG. 4D is a wave field plot at a later time subsequent to ultrasonictransmission showing the focusing of the ultrasonic wave front beyondthe tip of the acoustic waveguide and propagation of that ultrasonicwave front into the fluid emulsion;

FIGS. 5A-5D are ultrasound images of fluid flow generated by anultrasonic toothbrush with and without a waveguide;

FIG. 5A is a combined Doppler (inside the box) and B-mode (outside thebox) image depicting fluid flow induced by an ultrasonic toothbrushwithout an acoustic waveguide and without bristle tip motion (bristletips (BT) and bristle plate (BP) at the bottom of bristles);

FIG. 5B is a combined Doppler and B-mode image depicting fluid flowinduced by an ultrasonic toothbrush without an acoustic waveguide butwith bristle tip motion (MB) and demonstrating absence of any measurablefluid flow (FF) beyond the bristles;

FIG. 5C is a B-mode ultrasound image depicting fluid flow induced by anultrasonic toothbrush with an acoustic waveguide, wherein the waveguideis made to vibrate by a sonic component and showing that the vibratingacoustic waveguide generated a jet of bubbly fluid moving away from thetoothbrush head;

FIG. 5D is a Doppler and B-mode ultrasound image of the same ultrasonictoothbrush as described for FIG. 5C, further showing significant fluidflow (FF) and bubble (B) formation beyond the bristle tips;

FIG. 6 is a plot comparing the measured acoustic pressure levels at thetip of a flat versus a focused lens acoustic waveguide;

FIG. 7 is a plot showing the absorption of ultrasound waves transmittedthrough a dental fluid/bubble emulsion versus frequency;

FIG. 8 is a plot showing the percent of suspended red blood cellsdestroyed by shear stress induced by acoustic microstreaming associatedwith a stably oscillating bubble. The inset depicts a thin, hollow wirewith air in its center, placed within a vial of suspended red bloodcells;

FIGS. 9A-H depict geometries of various exemplary acoustic waveguidesfor use in the toothbrush heads of the present invention; and

FIG. 10 is a bar graph of data demonstrating the safety of a toothbrushaccording to the present invention, as measured using the cell lysisassay described in Example 5.

DETAILED DESCRIPTION

The present invention is based upon the discovery that a toothbrushemploying an acoustic waveguide, either alone or in combination with anultrasonic transducer and/or sonic component, yields improved cleaningproperties as compared to existing power toothbrush technologies. It iscontemplated that toothbrushes according to the present invention may ormay not include a number of conventional bristle tufts, as discussedbelow. In one embodiment, for example, a toothbrush employs a waveguidestructure in combination with bristle tufts and a sonic component forvibrating the waveguide structure and bristle tufts at sonicfrequencies. In another embodiment, a toothbrush employs an acousticwaveguide structure in combination with an ultrasonic wave generator. Inyet another embodiment, a toothbrush employs an acoustic waveguidestructure in combination with an ultrasonic wave generator and a soniccomponent.

As described in detail herein, toothbrushes according to the presentinvention are effective in (1) increasing bubbly fluid flow by motion,including sonic motion, of the acoustic waveguide and bubble formationby the waveguide and/or one or more toothbrush bristles; (2)transmitting focused ultrasonic waves generated by an ultrasonictransducer and propagating those waves through an acoustic waveguideinto the dental fluid to achieve improved plaque disruption and removal;and/or (3) facilitating bubbly fluid flow and transmitting ultrasound tointeract optimally and maximally at and beyond-the-bristles (e.g.,between about 0.5 mm and about 5 mm from the bristle tips, moretypically between about 1 mm and about 3 mm from the bristle-tips),within the dental fluid.

Thus, within certain embodiments, the present invention providestoothbrushes, including manual toothbrushes and power toothbrushes,comprising an acoustic waveguide. In certain embodiments of the presentinvention, toothbrushes are provided that comprise an acoustic waveguidein combination with an ultrasonic transducer that, together, act uponthe microscopic bubbly flow within the dental fluid, either as aconsequence of brushing with a bristled toothbrush head and/or themotion of the acoustic waveguide acted upon by the sonic component toinduce cavitation, acoustic streaming, and/or acoustic microstreamingwithin the dental fluid. Therefore, yet additional embodiments of thepresent invention provide toothbrushes comprising an acoustic waveguidein combination with an ultrasonic component and in further combinationwith a sonic component. The sonic component, in combination with anacoustic waveguide, being fabricated of a suitable material, and/or incombination with one or more toothbrush bristles, is further responsiblefor generating a favorable mouth feel, stimulating and massaging thegums and other dental tissue, and promoting an improved dental cleaningexperience.

All references to ranges of parameters described in this specificationare understood to include reference to a range equal to and greater thanthe lower value of each range, as well as ranges equal to and less thanthe higher value of each range. Thus, for example, the recitation of acarrier frequency of between about 250 and about 500 kHz in thisspecification is interpreted to include carrier frequencies of 250 kHzand greater; carrier frequencies of 500 kHz and less; as well as carrierfrequencies within the stated range. All U.S. and foreign patents andpatent applications and all other references cited herein are herebyincorporated by reference in their entireties.

Definitions and Parameters Governing the Operation of InventiveToothbrush Technologies

As used herein, the terms “ultrasound” or “ultrasonic” refer to acousticenergy, or sound, of a frequency higher than and outside of the normalaudible range of the human ear—generally of a frequency higher thanapproximately 20 kHz. Typically, ultrasonic transducers employed in thetoothbrushes of the present invention are capable of producingultrasonic frequencies within the range of about 20 kHz to about 5000kHz, more typically, from about 100 kHz to about 750 kHz, still moretypically, from about 250 kHz to about 750 kHz and, in some embodiments,from about 250-350 kHz. The term “sonic” refers to acoustic energy, orsound, of a frequency that is within the audible range of the humanear—generally up to about 20 kHZ—for example, between 20 Hz and 20 kHz.

As used herein, the term “cavitation” refers to the generation and/orstimulation of bubbles by sound. More specifically, the term“cavitation” is used herein to refer to the interaction between anultrasonic field in a liquid and in gaseous inclusions (e.g.,microbubbles) within the insonated medium. By “generation” is meant thecreation of bubbles; by “stimulation” is meant the action that causesthe bubbles to become dynamically active: that is, to move, to getbigger and smaller, to grow, to dissipate, all with associatedmechanical and/or chemical effects in and around the fluid surroundingthe bubbles and within the gas inside the bubbles.

Cavitation of existing microbubbles may be subdivided, to a firstapproximation, into two general categories—“stable cavitation” and“inertial cavitation.” “Stable cavitation” is the induction of stable,low-amplitude, resonant oscillations of preexisting microbubbles bylow-intensity ultrasound energy that, in turn, generates local shearforces within the fluid flow (referred to herein as acousticmicrostreaming) near and adjacent to the microbubbles. As the ultrasoundintensity is increased, the amplitude of oscillation also rises untilthe bubble becomes unstable and collapses due to the inertia of theinrushing fluid, giving rise to “inertial cavitation.”

The resulting extremes of pressure and temperature within a violentlycollapsing bubble (one typically more active than those required for thepresent invention) can be sufficient to initiate free radical generationby hydrolysis of contained water vapor. If bubble collapse occurs inproximity to a fluid/solid interface (for example, a dental surface),shear forces within the medium and high velocity fluid jets are directedtoward the solid structures, i.e., the teeth and gums. In the context ofthe present invention, cavitation effects include ultrasound-inducedstimulation of microbubbles already present in the dental fluid due tothe action of bristles into stable cavitation that, through theresulting scrubbing action from the shear forces associated withmicrostreaming, displaces or loosens plaque and other debris from dentalsurfaces and interproximal surfaces. Another effect can be thegeneration of coherent fluid flow away from the transducer, calledacoustic streaming, whose strength is enhanced by the interaction of theultrasound and microbubbles. Generally, ultrasonic transducersincorporated in toothbrushes of the present invention induce cavitationof microbubbles that are between about 1 μm and about 150 μm indiameter.

Toothbrushes of the present invention incorporating an ultrasoundtransducer and acoustic waveguide typically promote at least stablecavitation—that is, simple volumetric changes in bubbles where factorsin addition to and/or instead of the inertia in the surrounding fluidgovern the bubble behavior. Bubbles have a primary resonant frequencythat varies inversely with the bubbles' radius and also strongly dependson other factors, such as gas content and surface tension. Typically,for example, bubbles in dental fluid having a diameter of between about1 μm and about 150 μm resonate when ultrasound is applied to thosebubbles with an ultrasound transducer operating in the 20 kHz to 3 MHzrange. More typically, bubbles in dental fluid having a diameter ofbetween about 1 μm and about 100 μm resonate when ultrasound is appliedto those bubbles with an ultrasound transducer operating in the 30 kHzto 3 MHz range. Still more typically, bubbles in dental fluid having adiameter of between about 4.3 μm and about 33 μm resonate whenultrasound is applied to those bubbles with an ultrasound transduceroperating in the 100 kHz to 750 kHz range. Still more typically, bubblesin dental fluid having a diameter of between about 5 μm and about 30 μmresonate when ultrasound is applied to those bubbles with an ultrasoundtransducer operating in the 100 kHz to 600 kHz range. Still moretypically, bubbles in dental fluid having a diameter of between about6.5 μm and about 22 μm resonate when ultrasound is applied to thosebubbles with an ultrasound transducer operating in the 150 kHz to 500kHz range. In an exemplary toothbrush presented herein, bubbles indental fluid having a diameter of between about 12 μm and about 26 μmresonate when ultrasound is applied to those bubbles with an ultrasoundtransducer operating in the 250 kHz to 500 kHz range. Whether or not theapplied ultrasonic frequency differs from a bubble's resonant frequency,low levels of ultrasound induce temporal variations in bubble volumethat are initially small and sinusoidal, both within an acoustic cycleand over many acoustic cycles. And, whether or not the appliedultrasonic frequency differs from a bubble's resonant frequency, thoseinduced temporal variations in bubble volume generate movement withinthe fluid in proximity to the bubble, whose mechanical effects assist inand promote the removal of plaque.

Due to geometric properties and impedance mismatch, cavitating bubblesscatter and emit sound. Compression and rarefaction of a bubbleundergoing stable cavitation cause an emission of sound, primarily atthe frequency of the applied signal for low levels of ultrasound. Asbubbles grow toward their resonant frequency (which can happen in only afew cycles) or as the applied sound field increases, the volumetricchanges in the bubble evolve to more complex functions of time within anacoustic cycle, as do the acoustic emissions, whether or not thosechanges remain radially symmetric. As a function of growing bubbleamplitude, those emissions first include the superharmonics (2F0, 3F0,etc.) of the applied signal (F0) (as well as acoustic emissions of F0itself). Eventually, a once stabley-oscillating bubble may collapseviolently and/or become asymmetric, with an associated increase inamplitude of the superharmonic emissions as well as broadband acousticemissions (i.e., non-integral values of F0) over a greater range offrequencies, including the eventual emission of multiples of thesubharmonic of the applied signal (e.g., (½)F0). By detecting theseemissions—for example, via a hydrophone—the level of cavitation activitywithin insonified material can be remotely assessed and correlated witha variety of mechanical and chemical effects associated with cavitation,such as, for example, plaque removal, as demonstrated herein. See Changet al., IEEE Transactions on Ultrasonics, Ferroelectrics, and FrequencyControl 48(1):161-170 (2001); Poliachik et al., Ultrasound in Medicineand Biology 27(11):1567-1576 (2001); Leighton, Ultrasonics Sonochemistry2(2):S123-S136 (1995); and Roy et al., J. Acoust. Soc. Am87(6):2451-2458 (1990). For example, when divided by the amplitude ofthe applied signal, one can expect the normalized amplitude of thesuperharmonics to increase as bubble activity increases, with associatedincreases in plaque removal. In addition, one can expect the integralover the spectral emission band (from (½)F0 through 10F0, say) of thebubbly medium to increase as bubble activity increases, with anassociated increase in plaque removal.

As used herein, the terms “microstreaming” and “acoustic microstreaming”refer to the movement of fluid near and adjacent to microbubbles thatoccurs as a result of the action of mechanical pressure changes withinthe ultrasonic field on the microbubbles. In the context of the presentinvention, shear forces are associated with the cavitating microbubbleswithin dental fluid that are distributed along the surfaces of the gumsand teeth, as well as in interproximal and subgingival spaces. Theseshear forces, in turn, remove the plaque and/or stains on thesesurfaces.

Several ultrasound parameters contribute to producing “acousticmicrostreaming” in the context of toothbrushes of the present invention.The carrier frequency (i.e., the frequency of the individual ultrasoundwaves) is generally above about 20 kHz; typically between about 30 kHzand about 3 MHz; more typically between about 100 kHz and about 750 kHz;in some embodiments between about 100 kHz and about 600 kHz; in someembodiments between about 150 kHz and about 500 kHz; and, in someembodiments, between about 250 kHz and about 500 kHz. It will beunderstood that the actual, optimal range of the carrier frequency willdepend upon the available bubble population and the size of ultrasoundtransducer employed.

The “pulse repetition frequency” (“PRF”), i.e., the frequency of packetsor bursts of individual ultrasound waves, typically, though notexclusively, ranges from about 0.5 Hz and about 10,000 Hz; moretypically between about 0.5 Hz and about 2,500 Hz, and still moretypically between about 1 Hz and about 500 Hz. The desired PRF maydepend upon the ultrasound frequency, the number of cycles per burst andthe environment in which the toothbrush is operating, including themedium in which the ultrasonic energy is being used. In toothpaste, forexample, a preferred PRF at a 10% duty cycle is generally less thanabout 20 Hz and may be less than about 10 Hz. In an aqueous environment,though, a higher PRF may be used—typically over 40 Hz and in the rangeof between 40 to 200 Hz. In some embodiments of toothbrushes of thepresent invention that use ultrasound frequencies in combination withsonic frequencies, the PRF is a small multiple (generally two orgreater, more typically four or greater) of the sonic frequency (i.e.,the frequency of movement of the bristles and/or acoustic waveguidedriven by a sonic component of a toothbrush of the present invention).

The number of individual ultrasound waves within a packet or burst ofultrasound (cycles per burst) is typically between about 10 and about10,000; for many embodiments between about 500 and 10,000. The desirednumber of cycles per burst depends upon the ultrasound frequency, thePRF, and the environment in which the toothbrush is operating. Forpromoting acoustic microstreaming in the context of toothbrushes of thepresent invention, relatively long bursts and relatively low PRF aresuitable. The product of PRF and burst duration yields the duty cycle(i.e., the percentage of time that the ultrasound is activated).Typically, the duty cycle is between about 1% and about 15%. Theultrasonic components of toothbrushes of the present inventionpreferably operate within these ranges.

Preferred ultrasonic operating parameters depend, as described above, onseveral interrelated factors, including the ultrasonic frequency, thePRF, the number of cycles per burst, the duty cycle, and the environmentin which the device is operated. For devices operated in a toothpasteemulsion environment, the combinations of operating parameters describedin the table below are suitable. Ultrasound Frequency Range Cycles/BurstPRF (Hz) Duty Cycle 100-750 kHz 500-10,000 0.5-75  5% 100-750 kHz500-10,000 1.0-150 10% 100-750 kHz 500-10,000 1.5-225 15% 250-500 kHz500-10,000 1.3-50  5% 250-500 kHz 500-10,000 2.5-100 10% 250-500 kHz500-10,000 3.8-150 15% 300 kHz 500-10,000 1.5-30  5% 300 kHz 500-10,0003.0-60  10% 300 kHz 500-10,000 4.5-90  15%

For devices operated in a water environment, the combinations ofoperating parameters described in the table below are suitable.Ultrasound Frequency Range Cycles/Burst PRF (Hz) Duty Cycle 100-750 kHz50-1,000 5-750 5% 100-750 kHz 50-1,000 10-1500 10% 100-750 kHz 50-1,00015-2250 15% 250-500 kHz 50-1,000 12.5-500   5% 250-500 kHz 50-1,00025-1000 10% 250-500 kHz 50-1,000 37.5-1500   15% 300 kHz 50-1,00015-300  5% 300 kHz 50-1,000 30-600  10% 300 kHz 50-1,000 45-900  15%

In yet another embodiment, a toothbrush of the present invention havingan ultrasound transducer operates at an ultrasound frequency of from250-350 kHz, at a duty cycle of about 10% with about 5,000 cycles perburst at a pulse repetition frequency of about 6 Hz. In yet anotherembodiment, a toothbrush of the present invention having an ultrasoundtransducer operates at an ultrasound frequency of from 250-350 kHz, at aduty cycle of about 10% with about 500 cycles per burst at a pulserepetition frequency of about 60 Hz.

As used herein, the term “acoustic streaming” refers to the bulk orcoherent flow of fluid that occurs due to momentum transfer from anacoustic wave to a fluid as a result of attenuation of an ultrasoundbeam. Ultrasound propagating into fluid, with or without bubbles, cangenerate “acoustic streaming,” which can be quite significant in sizeand extent, and even greater with than without bubbles in the fluid.Acoustic streaming generally requires higher frequencies than requiredfor stimulating the bubbles—the higher the frequency, the greater theacoustic streaming.

The acoustic streaming velocity, V, is proportional to the amplitudeabsorption coefficient, α, of the fluid, which is itself proportional tothe frequency of the ultrasound under linear acoustic propagationconditions, and even more strongly dependent upon frequency undernonlinear acoustic propagation conditions, and inversely proportional toits kinematic viscosity, ν, as follows:V=(αl ² I/cν)(G)where I is the intensity in the beam of ultrasound and l the ultrasoundbeam diameter, c is the velocity of sound and G is a geometric factorthat depends upon the size of the acoustic beam. Zauhar et al., BritishJ. of Radiology 71:297-302 (1998).

Ultrasound operating parameters for promoting “acoustic streaming” inthe context of toothbrushes of the present invention may vary from thoseemployed for promoting acoustic microstreaming. The ultrasoundparameters that generally promote acoustic streaming include a carrierfrequency typically greater than about 20 kHz; more typically, betweenabout 500 kHz and about 5,000 kHz or more, to enhance acousticabsorption. The pulse repetition frequency (“PRF”) is typically, thoughnot exclusively, between about 1 Hz and about 10,000 Hz; more typicallybetween about 10 Hz and about 10,000 Hz; still more typically betweenabout 100 Hz and about 10,000 Hz; and yet more typically, between about1,000 Hz and about 10,000 Hz. The number of individual ultrasound waveswithin a packet or burst of ultrasound is typically between 1 and 5,000cycles/burst; more typically between about 5 and about 100 cycles/burst.To enhance “acoustic streaming,” longer duty cycles are typical, suchas, for example, at least about 10%; more typically between about 25%and about 100%; still more typically between about 50% or about 75% andabout 100%. Longer bursts, e.g., greater than about 100 waves at afrequency of about 1 MHz, with a PRF of at least 1,000 Hz, areexemplified herein.

As used herein, the term “mechanical index” refers to a measure of theonset of cavitation of a preexisting bubble subjected to one cycle ofapplied acoustic pressure. Holland et al., IEEE Transactions onUltrasonics, Ferroelectrics, and Frequency Control 36(2):204-208 (1989);and Apfel et al., Ultrasound Med. Biol. 17(2):179-185 (1991). Thismeasure is proportional to the peak negative pressure (MPa) amplitudeand inversely proportional to the square root of the frequency (MHz) ofthe applied sound. When the value of mechanical index exceeds 1.9, it ispossible for ultrasound to produce inertial cavitation, the mostmechanically active type of cavitation, which is in excess of the amountrequired to remove plaque. The governing assumptions require isothermalgrowth of an optimally sized bubble, the neglect of gas diffusion intothe bubble, and that the fluid surrounding the bubble is incompressible.These three assumptions produce the most active bubble collapse, makingthe mechanical index a conservative measure of the onset of inertialcavitation.

Empirical evidence indicates that plaque removal may be achieved withmechanical indices as low as 0.1. Theoretical considerations, however,suggest that plaque reduction may be achieved with mechanical indices aslow as 0.01. Krasovitski et al., IEEE Transactions on Ultrasonics,Ferroelectrics, and Frequency Control 51(8):973-979 (2004). For example,the shear stress on a wall created by acoustic microstreaming associatedwith a bubble suspended in water and subjected to ultrasound at afrequency of 430 kHz and pressure amplitude of 10,000 Pa (e.g., amechanical index of approximately 0.01) is predicted to be approximately5 Pa, which is sufficient to remove plaque via steady flow over plaque.Stoodley et al., J. Industrial Microbiology & Biotechnology 29:361-367(2002). The mechanical indices delivered by toothbrushes of the presentinvention are generally in the range of about 0.001 to about 1,000. Moretypically, mechanical indices are in the range of about 0.001 to about100, still more typically in the range of about 0.002 to about 20, andeven more typically in the range of about 0.01 to about 5, or betweenabout 0.01 and about 1.9. Toothbrushes delivering mechanical indices ofless than about 1.9, more typically less than about 1.5, and frequentlyless than about 1.2 are contemplated by the present invention.

The acoustic output of an ultrasound device, measured as the peaknegative acoustic pressure, is related to the mechanical index. Suitableoperating peak negative acoustic pressure parameters in toothbrushes ofthe present invention are generally in the range of from about 0.01 to100 MPa; more typically in the range of from 0.1 to 10 MPa; for manyembodiments in the range of from 0.1 to 1 MPa; for many embodiments inthe range of from 0.25 to 0.6 MPa; and in yet other embodiments in therange of from 0.3 to 0.5 MPa.

As used herein, the term “microbubble” refers to microscopic bubblespresent in the oral cavity, for example, in the dental fluid or plaque.“Microbubbles” may be endogenous to the fluid, such as through theintroduction of an appropriate dentifrice; may be generated bytoothbrush bristles through manual brushing; and/or may be generated bybristles in combination with the sonic component of certain of thepresently disclosed power toothbrushes. “Microbubbles” are acted upon byan ultrasonic signal transmitted by an ultrasonic transducer andpropagated by an acoustic waveguide. “Microbubbles” resonate at or neara specific frequency depending upon the microbubbles' diameter.

An Exemplary Toothbrush

FIG. 1A shows an exemplary toothbrush 10 according to the presentinvention. The toothbrush 10 comprises a handle 15 constructed of arigid or semirigid material, and typically houses a rechargeable battery12 that is preferably adapted to be induction charged; electricalcircuitry, including an ultrasonic module drive circuit 14; a soniccomponent 16 comprising a motor, preferably a DC motor for driving atoothbrush head 20 at sonic frequencies; and a timer and motor controlunit 18. Suitable motors, ultrasonic drive circuits, rechargeablebatteries, and timer and motor control units are well known in the art.

Attached to the handle 15 is a toothbrush head 20 including a supportstructure including a stem portion 21 and further comprising anultrasonic transducer 22 and an acoustic waveguide 24 in operableproximity and acoustically coupled to the ultrasonic transducer 22. Inthe toothbrush embodiment presented in FIG. 1A, an ultrasound reflectionelement 28 is shown behind, and extending around each side of, theultrasonic transducer 22. It will be appreciated that the ultrasoundreflection element 28 at least partially reflects the ultrasound throughthe acoustic waveguide 24 and into the dental fluid. The toothbrush head20 may be either removably or fixedly attached to the handle 15. Ingeneral, the toothbrush head 20 includes a plurality of bristle tufts 26retained by the support structure 21 and disposed generally adjacent to,or near to, the acoustic waveguide 24. The toothbrush head 20 mayoptionally include an impedance matching layer 29. The impedancematching layer 29 improves the efficiency of the device, as discussedbelow.

In the disclosed embodiment, alternating current supplied by theultrasonic module drive circuit 14 drives the ultrasonic transducer 22such that the transducer 22 expands and contracts primarily along oneaxis at or near resonance with the frequency supplied by the ultrasonicmodule drive circuit 14, thereby converting electrical energy intoultrasonic energy. The resulting ultrasonic sound waves are conductedinto, propagated through, focused by, and radiated out of the acousticwaveguide 24. The focused ultrasonic energy acts on microbubbles withinthe dental fluid (typically saliva and dentifrice, not shown) to inducecavitation, thereby loosening plaque deposited on the teeth and ininterproximal regions.

The Ultrasonic Transducer and Module

As described above, certain embodiments of the present invention providea toothbrush 10 that employs an ultrasonic transducer 22 to generateultrasonic energy in combination with an acoustic waveguide 24 toefficiently propagate that ultrasonic energy into the dental fluid.Microbubbles, either present in the dental fluid through conventional,manual brushing action with a manual toothbrush and/or formed by actionof a sonic component 16 driving the motion of the toothbrush bristletufts 26 and/or acoustic waveguide 24 at sonic velocities (see below),are stimulated through ultrasonic energy-induced cavitation to achieve“scrubbing bubbles” that are effective in loosening and removing plaquefrom a tooth surface and interproximal regions at a finite distance fromthe toothbrush head.

Absent action of the ultrasonic transducer 22 of the present invention,microbubbles are simply passive voids within the dental fluid. Theultrasonic transducer 22 disclosed herein causes these microbubbles topulsate, thereby generating local fluid motion around the individualbubbles. This effect is referred to herein as “microstreaming” and, incombination with the ultrasonic cavitation effects, achieves shearstresses that are sufficient to disrupt plaque. Typically, shearstresses achieved by microstreaming induced by the ultrasonic transducer22 of the present invention, are between about 0.1 Pa and about 1,000Pa. More commonly, shear stresses achieved by microstreaming are betweenabout 0.2 Pa and about 500 Pa. Still more commonly, shear stresses arebetween about 0.3 Pa and about 150 Pa. And most commonly, shear stressesare between about 1 Pa and about 30 Pa.

Another effect of the ultrasonic transducer 22 is that it promotesacoustic streaming and produces momentum within the dental fluid in adirection toward the teeth and interproximal and subgingival spaces,thereby increasing the velocity and coherency of the dental fluid. Thisbulk fluid-flow process is referred to herein as acoustic streaming.Either through the generation of acoustic microstreaming and/or acousticstreaming, the associated shear and pressure forces act to erode anddislodge the plaque in a manner and to an extent that is in excess ofthat achieved by the toothbrush bristle tufts 26 alone. In particular,these ultrasonic effects are facilitated by propagating the ultrasonicwaves from the ultrasonic transducer 22 through an acoustic waveguide 24and into the dental fluid near and beyond the tips of bristle tufts 26.

Ultrasonic transducers 22 that may be suitably employed in theultrasonic toothbrush 10 of the present invention are readily availablein the art (see, for example, U.S. Pat. No. 5,938,612 and No. 6,500,121,each of which is incorporated herein by reference in its entirety) and,most commonly, operate either by the piezoelectric or magnetostrictiveeffect. Magnetostrictive transducers can, for example, produce highintensity ultrasonic sound in the 20-40 kHz range. Alternatively,ultrasound may be produced by applying the output of an electronicoscillator to a thin wafer of piezoelectric material, such as leadzirconate titanate (PdZrTi or PZT). There is a wide variety ofpiezoelectric PZT ceramic blends that can be used to fabricateultrasonic transducers suitable for use in the toothbrushes of thepresent invention. Other transducer materials, such as piezopolymers,single or multilayer polyvinylidene fluoride (PVDF), or crystallinepiezoelectric materials, such as lithium niobate (LiNbO₃), quartz, andbarium titanites, may also be used. Ultrasound transducers may be flator curved (as, e.g., in a conic section) to focus the ultrasonic waves.

In addition to piezoelectric materials, capacitive micromachinedultrasonic transducer (cMUT) materials or electrostatic polymer foamsare also suitable. Many of these materials can be used in a variety ofvibrational modes, such as radial, longitudinal, shear, etc., togenerate the acoustic waves. In addition, single-crystal piezoelectricmaterials, such as Pb(Mg_(1/3)Nb_(1/3))O₃—PbTiO₃ (PMN-PT),K_(1/2)Na_(1/2)NbO₃—LiTaO₃—LiSbO₃ (KNN-LT-LS) as described in Lead-freepiezoelectric ceramic in the K_(1/2)Na_(1/2)NbO₃ solid solution system,N. Marandian Hagh, E. Ashbahian, and A. Safari presented at the UIAsymposium March 2006, and others, may be used to reducevoltage/transmit-level ratios by as much as an order of magnitude.

In addition to the transducer materials, one or multiple impedancematching layers 29 (typically designed as quarter-wave matching layers)can help to improve the efficiency and bandwidths when transmitting fromthe commonly high-impedance transducer materials into the much lowerimpedance acoustic waveguide materials. Generally, a matching materialis chosen with a thickness that will support a quarter wave of thedesired frequency and an acoustic impedance optimally selected withinthe two impedances to be matched. Appropriate materials can includematerials such as epoxy and metal particulate composites, graphite, or ahost of other candidate materials known by and readily available to theskilled artisan.

In one embodiment, as illustrated in FIG. 1B, an ultrasound transducersuitable for use in toothbrushes of the present invention comprises twoor more piezoelectric elements. In a currently preferred embodiment theultrasonic transducer 30 has a rectangular or trapezoidal profile andincludes two piezoelectric elements 32 and 34 with one or moreelectrical contact(s) 36 contacting the piezoelectric elements and inelectrical contact with an ultrasonic module drive circuit 14 (FIG. 1A)handle 15. The ultrasonic module drive circuit 14 may be placedelsewhere in the apparatus, for example in the brush head 20. Thepiezoelectric elements 32, 34 are stacked in series mechanically, andconnected in parallel electrically. Mechanical stacking the elements inseries provides that the displacements associated with the individualpiezoelectric elements 32, 34 are added. Electrically connecting thepiezoelectric elements 32, 34 in parallel provides that the capacitanceassociated with the individual piezoelectric elements 32, 34 are alsoadditive. This provides a greater range of electronics drivingpossibilities.

The ultrasonic transducer 30 may also comprise an impedance matchinglayer 38 and one or more mounting prongs 40 for interaction with anacoustic waveguide and/or to facilitate placement of the transducer 30in the brush head 20. Although a generally rectangular ultrasonictransducer 30 structure is illustrated, it will be appreciated thatpiezoelectric elements and transducer structures may be provided in avariety of two and three dimensional configurations and thatnon-rectangular ultrasonic transducer structures may be used intoothbrushes without departing from the present invention.

It is contemplated that the ultrasonic transducer 30 may be provided asa component of an ultrasound generator module designed for installationin toothbrushes of the present invention, the module including one ormore piezoelectric crystal(s) with attached electrodes, one or moreoptional matching layer(s), one or more acoustic waveguide(s), and asupporting structure. The supporting structure is designed to directultrasonic wave propagation through the optional matching layer(s) andwaveguide. This may, for example, be accomplished by selecting thesupporting structure coupling features to coincide with areas of minimalmotion (nodal mounting) on the piezoelectric ceramic, matching layer,and waveguide. In one embodiment, the acoustic waveguide has a baseportion that is mounted over the transducer assembly and extends fromthe transducer assembly. One suitable mounting orientation, for example,is to locate the ultrasound transducer in the body of the brush headwith the acoustic waveguide extending from the-base of the brush head inthe same direction as the bristle tufts. The transducer module generallyresides within the toothbrush head and is replaced with the bristles andbrush head when the toothbrush head exceeds its useful life.

Additional waveguide supporting structures may also be provided asstructural features of the transducer module or the brush headstructure. A waveguide support flange may be provided in proximity tothe perimeter of the waveguide structure extending from the brush base,for example, to provide a rigid structure supporting the base of thewaveguide.

Regardless of the precise configuration of the individual elements thatcomprise the ultrasound module, the piezoelectric element, matchinglayer and/or the waveguide shape are generally designed to focus theacoustic energy at a desired location relative to the emanating surfaceor to disperse the acoustic energy in a specific beneficial pattern. Theultrasonic energy may, for example, radiate directly from a generatingsource such as a piezoelectric ceramic element directly into the oralcavity fluid without an intervening matching layer or waveguide.Alternatively, an acoustic waveguide may be placed directly on thepiezoelectric ceramic. In still further embodiments, the entireultrasonic module, including the acoustic waveguide, are fabricated froma piezoelectric polymer.

The following section describes the acoustic waveguide structure ingreater detail.

The Acoustic Waveguide Structure

As indicated above, one aspect of the present invention is based uponthe observation that an acoustic waveguide used in operable combinationwith an ultrasonic transducer is effective in propagating ultrasonicwaves from the transducer into the dental fluid, thereby generatingand/or causing cavitation of microscopic bubbles (microbubbles) presentwithin the dental fluid. Typically, as shown in FIG. 1A, the ultrasonictransducer 22 is positioned at the base of the toothbrush head 20, inoperable proximity and acoustically coupled to the acoustic waveguide24, such that ultrasonic waves are efficiently propagated into andthrough the acoustic waveguide 24 and into the dental fluid (not shown).As noted above, within certain embodiments, the present invention alsoprovides power toothbrushes 10 comprising a toothbrush head 20 having anacoustic waveguide 24 wherein the toothbrush head 20 is operablyconnected to a sonic component 16 and wherein the sonic component 16causes the acoustic waveguide 24 to vibrate so as to increase the flowand generation of microbubbles in the dental fluid into which theacoustic waveguide 24 is immersed during use.

Within still further embodiments are provided power toothbrushes 10comprising a combination of an acoustic waveguide 24 in operableproximity to an ultrasonic transducer 22 and operably connected to asonic component 16 to achieve still further improved dental cleaningproperties owing to the combined increase in fluid flow and microbubbleformation, as well as cavitation and acoustic microstreaming effects.Here, operable connection can be facilitated by putting the ultrasonictransducer 22 in direct contact with the acoustic waveguide 24 or,alternatively, ultrasound conducting material such as an impedancematching layer 29 can be placed between the ultrasonic transducer 22 andthe acoustic waveguide 24 both to increase the efficiency of ultrasoundtransmission from the transducer 22 into the acoustic waveguide 24 or,alternatively or additionally, to usefully increase the distance betweenthe transducer 22 and the acoustic waveguide 24 to facilitate themanufacturing process of the device, for example.

The acoustic waveguide provides a conduit for the transmission ofultrasonic waves from the ultrasonic transducer, where they aregenerated, through an (optional) impedance matching layer, to the fluidin the oral cavity. The acoustic waveguide, in general, has a size andprofile that is substantially larger than that of an individual bristleor bristle tuft and is substantially more effective in deliveringultrasonic energy to the fluid in the oral cavity. The length of thewaveguide is, typically, a factor of approximately 1.5-2.5 times thewavelength of the ultrasonic waves in the waveguide medium multiplied,although the length may vary in increments of approximately one-halfwavelength to achieve efficient ultrasound wave propagation. The actualheight and width of the acoustic waveguide is determined by designparameters such as the ultrasound transducer face area, mountingconsiderations, and aesthetic requirements.

FIG. 1C illustrates an exemplary acoustic waveguide structure 50 incombination with the exemplary ultrasonic transducer 30 shown in FIG.1B. The waveguide structure 50 comprises a base structure 52 sized to(at least partially) cover the ultrasound transducer 30 and having aconfiguration generally matching that of the ultrasound transducer. Basestructure 52 is generally mounted and anchored in a toothbrush head 20(FIG. 1A) with distal waveguide portion 54 extending outwardly from thebrush head structure. The waveguide structure 50 is preferably a unitarystructure having a generally block-like three-dimensional configurationhaving multiple faces. In the embodiment illustrated, thecross-sectional area of base structure 52 is generally larger than thecross-sectional area of distal waveguide portion 54 and opposing sidewalls 56 and end walls 58 are tapered and terminate distally in a distalwaveguide face 60. Distal waveguide face 60 may be curved in a generallyconvex configuration, as illustrated in FIG. 1C. In alternativeembodiments, distal waveguide face 60 may be generally flat, curved in agenerally concave configuration, or curved in a more complexconfiguration. The intersections of one or more of the waveguide facesmay be rounded or chamfered, as shown, or they may form angular corners.Additional waveguide embodiments are described in greater detail below.

Rigid acoustic waveguides, such as solid waveguides made from aluminumor titanium, and hollow waveguides filled with degassed water, have beendescribed for the delivery of high intensity focused ultrasound (HIFU)into living tissue for therapeutic purposes (such as drug delivery andhemostasis) via heat induction and/or for the generation of inertialcavitation. See, e.g., U.S. Patent Publication No. 2003/0060736 toMartin et al. and Mesiwala et al., Ultrasound in Medicine and Biology28(1):389-400 (2002). These applications for acoustic waveguidesdemonstrate the use of a physical member to facilitate propagation ofultrasound beyond the face of an ultrasound transducer to achievetherapeutic benefit. The currently preferred waveguide structure is, incontrast, based upon the observation that acoustic waveguides comprisinga flexible member, typically having a flat profile, may be employed incombination with an ultrasound transducer to facilitate propagation ofultrasound into the oral cavity to stimulate existing bubbles to removeplaque in a way that also optimally generates a bubbly fluid jet (due tothe flat aspect of the profile) and promotes a favorable mouth feel.

The dental fluid into which the acoustic waveguide is immersed duringuse is typically a saliva and toothpaste emulsion that is veryacoustically absorptive due to the presence of large air pockets withinindividual bristle tufts and between neighboring bristle tufts and,without the use of an acoustic waveguide, would attenuate significantamounts of the ultrasound before the wave front reached the tooth andgum surfaces. The air medium has very low acoustic impedance, whichcreates a large impedance mismatch with the high acoustic impedancematerials generally used in the ultrasonic transducer. This impedancemismatch is a significant barrier to sound transmission from theultrasonic transducer to the tooth and gum surfaces. The acousticwaveguide serves as a bridge across this acoustic mismatch by accepting,containing, and transmitting the acoustic energy into the saliva andtoothpaste emulsion near the tooth surface, thereby overcoming theattenuation effect normally encountered by the saliva and toothpasteemulsion.

A variety of acoustic waveguide designs are contemplated by the presentinvention as exemplified by the acoustic waveguides illustrated in FIGS.2-5 and 9A-9H. Depending upon the precise embodiment of the presentinvention, the acoustic waveguide may be used alone, in combination witha sonic component, and/or in combination with an ultrasonic transducer.Suitable acoustic waveguides have in common the capacity to physicallymove the dental fluid and/or to efficiently facilitate the propagationand possibly the focusing of ultrasonic waves transmitted by theultrasonic transducer, thereby enhancing fluid motion and the associatedeffects of the resulting cavitation and microstreaming.

FIG. 2A shows an embodiment of an exemplary power toothbrush head 120comprising an ultrasonic transducer 122 in combination with an acousticwaveguide 124. The side view shows the acoustic waveguide 124, whichcarries the ultrasonic energy from the ultrasonic transducer 122 to theteeth and gums (not shown). Acoustic waveguide 124 is in operableproximity and acoustically coupled to the ultrasonic transducer 122 andadjacent to and flanking, on one or more sides, bristle tufts 126. Thesize and configuration of the base of acoustic waveguide 124, in thisembodiment, generally matches the size and configuration of ultrasonictransducer 122 and/or impedance matching layer 129. The tip of acousticwaveguide 124 distal from the ultrasonic transducer 122 has a smallercross-sectional area than that of the base of acoustic waveguide 124 inproximity to ultrasonic transducer 122.

The acoustic waveguide 124, in the embodiment illustrated in FIG. 2A,has one dimension oriented generally along the longitudinal axis of thebrush head 120 (the length), that is wider than the diameter of abristle tuft 126 and, more preferably, has a length that is greater thanthe (side-to-side) combined diameters of two bristle tufts 126. Inanother embodiment, the length of the acoustic waveguide 124 is greaterthan the (side-to-side) combined diameters of five bristle tufts 126. Inanother dimension, the width of the acoustic waveguide 124 (orientedgenerally transverse to the longitudinal axis of the brush head 120 asshown in FIG. 2A) at its base is generally greater than the diameter ofa bristle tuft 126 and, in some embodiments, is generally greater thanthe (side-to-side) combined diameters of at least two bristle tufts 126.

In one embodiment, the height of the acoustic waveguide 124 exposed whenthe waveguide is mounted in the brush head 120 is less than the exposedheight of at least one bristle tuft 126 and, in another embodiment, theheight of the acoustic waveguide 124 exposed when the waveguide ismounted in the brush head 120 is less than the exposed height of each ofthe bristle tufts 126. In another embodiment, the height of the exposedacoustic waveguide 124 portion is greater than at least one bristle tuft126 provided in the brush head 120. In general, the exposed height ofthe acoustic waveguide is greater than about 50% and less than about120% of the exposed height of the bristle tufts 126. In yet anotherembodiment, the exposed height of the acoustic waveguide 124 is greaterthan about 70% and less than about 110% of the exposed height of thebristle tufts 126. In some embodiments, the cross-sectional area ofwaveguide 124 at its distal face is at least five times greater thanthat of a bristle tuft 126; in another embodiment, the cross-sectionalarea of waveguide 124 at its distal face is at least ten times greaterthan that of a bristle tuft 126; and in another embodiment, thecross-sectional area of waveguide 124 at its distal face is at leasttwenty times greater than that of a bristle tuft 126. In this exemplarydesign, the acoustic waveguide 124 is made from a soft, smooth material,such as silicone rubber, known for both its pleasant surface texture andability to transmit ultrasound. Impedance matching layer 129 is disposedbetween acoustic waveguide 124 and ultrasonic transducer 122.

Two parameters that substantially affect the transmission of ultrasonicwaves through an acoustic waveguide are (1) the material from which thewaveguide is fabricated, and (2) the geometry of the waveguide. Each ofthese parameters is described in further detail herein. Regardless ofthe precise acoustic waveguide material and geometry employed, thepresent invention contemplates the selection of parameters to achieve afavorable mouth feel. Thus, the material from which the acousticwaveguide is fabricated or molded is preferably soft enough to beappealing when placed within the mouth and/or direct contact with themouth. As will be appreciated by one skilled in the art, an acousticwaveguide with an appealing texture is ideally designed to efficientlycouple in, conduct, coherently focus, incoherently compress, and coupleout the acoustic energy.

The selection of suitable materials for fabricating an acousticwaveguide for use in a toothbrush of the present invention can bereadily achieved by the skilled artisan in consideration of thefollowing guidelines. Various dielectric materials, such as silicondioxide (SiO₂), silicon nitride (Si₃N₄), and many polymers can be usedas the waveguide material. For example, silicone rubber and other typesof rubbers, silicone materials such as castable/moldable RTV, liquidinjection-molded (LIM) silicone, thermoplastic elastomers, thermalplastic elastomer (TPE) injection-molded processes, and closed or opencell foams may all be used. Polymers have an advantage over otherwaveguide materials, owing to their relatively low shear wave velocity.However, because of their viscoelasticity, cross-linking may benecessary to avoid excessive acoustic loss and provide equilibriumelastic stress, thus providing a more stable waveguide layer.

The hardness of materials suitable for use in acoustic waveguides of thepresent invention may be determined by either the Shore (Durometer) testor the Rockwell hardness test. Both of these hardness test methodologiesare well known and readily available in the art. These tests measure theresistance of materials to indentation and provide an empirical hardnessvalue. Shore hardness, using either the Shore A or Shore D scale, is thepreferred method for rubbers/elastomers and is also commonly used for“softer” plastics, such as polyolefins, fluoropolymers, and vinyls. TheShore A scale is generally used for “softer” rubbers, while the Shore Dscale is generally used for “harder” materials. Shore hardness ismeasured with a Durometer and, consequently, is also known as Durometerhardness. The hardness value is determined by the penetration of theDurometer indenter foot into the sample. The ASTM test methoddesignation is ASTM D2240. Related methods include ISO 7619, ISO 868,DIN 53505, and JIS K 6253. Each of these Durometer test methodologies ishereby incorporated by reference in their entireties.

The Durometer measurement of acoustic waveguides employed intoothbrushes of the present invention generally range in hardness from 5Shore A to 60 Shore D, more typically from 10 to 100 Shore A, and stillmore typically from 10 to 65 Shore A. An acoustic waveguide hardness ofapproximately 40 Shore A or less is preferred for many applications toprovide oral comfort. It will be apparent to the skilled artisan thatharder materials may be employed in the acoustic waveguides used inconjunction with the power toothbrushes of the present invention;however, harder materials may provide a progressively unpleasant mouthfeel. The waveguide material may have isotropic or anisotropicproperties or, in an alternative embodiment, may comprise one materialhaving isotropic properties and another material having anisotropicproperties.

The present invention also contemplates that more than one material maybe used in combination to achieve acoustic waveguides having preferredproperties of hardness and mouth feel and providing an acousticimpedance matching function. Different materials may be provided asmultiple layers forming a unitary component, or different materials maybe provided in selected locations to impart desired material andacoustic properties, the latter including, for example, focusing of theultrasound emitted from the transducer to a point at and near theaverage distance from the distal tip of the waveguide to the toothsurfaces within the interproximal space and/or the lingal or buccalsurfaces of the teeth. For example, additional acoustic matchingelements may be embedded or stratified within the acoustic waveguidestructure and be in operable contact with the ultrasonic transducer viaone or more matching layers. Within certain embodiments, acousticwaveguides of the present invention further provide a matching layer atthe waveguide tip to help coupling into low impedance toothpasteemulsions (e.g., dental fluid). Ideally, there will also be asignificant specific acoustic impedance change between the sides of theacoustic waveguide and the surrounding medium such that the waves arenot coupled substantially into the surrounding medium by the sides ofthe acoustic waveguide. In one embodiment, a matching layer of graphite,mineral, or metal-filled epoxy is provided between a ceramic transducerelement and the waveguide. Another embodiment may combine the functionsof a matching layer and waveguide by fabricating a stratified part withvarying acoustical impedance in the direction of wave propagation. Thevariation in acoustical impedance of the acoustic waveguide may be alinear or nonlinear function.

Exemplified herein are prototype transducer assemblies having a graphiteimpedance matching layer in operable contact with a piezoelectricultrasonic transducer. As shown in FIG. 9A, a waveguide assembly 150Amay include a graphite core portion 152A or similar material that may beinserted into an injection mold, and an elastomer outer portion 154Amolded or otherwise provided around it using, for example, the processof insert molding. Alternatively, a multishot technique may be used tocreate a gradient of materials with different acoustic and elastomericproperties. As used herein, the term “multishot” refers to the placementof several shots of thermoplastic material into one mold. This processmay be employed, for example, in acoustic waveguide embodiments in whicha first relatively hard material layer (e.g., about Shore 80 hardness orgreater) is in operable proximity to the ultrasonic transducer element;a second, relatively soft material layer (e.g., between about Shore 20and Shore 80) is immediately adjacent to and in contact with the firstmaterial layer; and a third, still softer (e.g., about Shore 20 hardnessor less) material layer is immediately adjacent to and in contact withthe second layer, for a very gentle feel against teeth. These exemplaryacoustic waveguide designs may either be formed as individual pieces or,alternatively, they may be molded in combination with the materialforming the toothbrush head and/or the support for the bristles.

In preferred embodiments, acoustic waveguides of the present inventionare substantially free from unfilled or gas-filled voids. To the extentthat multiple materials are used to form a waveguide, those materialsgenerally contact each other closely without allowing the formation ofair gaps between surfaces. For some embodiments, however, it may bedesirable to form one or more voids in the acoustic waveguide andsubstantially fill the voids with a material that has good acoustictransmission properties at the ultrasound operating parameters describedherein.

Thus, within certain embodiments, acoustic waveguides of the presentinvention may comprise two or more plastic/elastomer layers. Forexample, acoustic waveguides comprising three, four, and/or fiveplastic/elastomer layers are contemplated for certain applications. Suchacoustic waveguides may further comprise one or more inserted pieces forshaping the acoustic properties and optimizing sonic properties. Onefunction of an acoustic waveguide used in combination with an ultrasoundtransducer is to focus the ultrasound, as described above. In oneembodiment, rigid or semi-rigid layer may be positioned in front of(distal to) the matching layer to provide improved acoustic properties.Using this type of intermediate layer allows a lower durometer elastomerwaveguide to provide a softer feel to the teeth under sonic conditions,which is preferred for some embodiments.

Referring now to FIGS. 9A-9H, it will be appreciated by the artisan thatacoustic waveguides may be formed in any of a variety ofthree-dimensional shapes or geometries. For example, FIG. 9A shows awaveguide 150A having a generally curved and tapered geometry. The twoopposing sidewalls of waveguide 150A taper from a wider base portion toa narrower tip portion and are generally planar, having a symmetricalcurved profile. The taper angle, defined as the angle between a lineextending perpendicularly from the base and the sidewall, is generallyfrom about 0.5° to about 20°, more generally from about 1° to about 10°,and the taper angle of each side wall is generally substantially similarand in an opposite direction. The distal face of waveguide 150A isgenerally symmetrically curved and generally semi-circular. Inalternative embodiments, the waveguide edge may be asymmetrically curvedor may form multiple curved apexes having the same or differentdimensions and configurations.

FIG. 9B illustrates an alternative waveguide 150B having a generallyrectangular portion and a converging or wedge-shaped portion 152B. Thegenerally rectangular portion forms a base that is mounted in proximityto the acoustic waveguide. The taper angle of the side walls forming thewedge-shaped portion 152B is generally from about 5° to about 65°, moregenerally from about 10° to about 45°, and the taper angle of each sidewall is generally substantially similar and in an opposite direction.The faces of the side walls are generally rectangular rather thanpresenting a curved profile. The edges of the sidewalls may be chamferedor curved to provide a softer mouth feel. In the embodiment illustrated,the base portion and the tapered portion are generally equivalent inheight. It will be appreciated that the relative dimensions of eachportion may vary, depending on the properties of the materials used, thephysical and geometrical properties of the underlying ultrasoundtransducer, and the acoustic transmission properties desired.

FIG. 9C shows an alternative waveguide 150C, wherein a convergingportion comprises a plurality of sections 152C that may be separated bygaps 154C. The waveguide sections and gaps may be spaced symmetricallyor asymmetrically and may have uniform or different sizes. In otherwords, one or more of the waveguide sections may have a differentprofile or different dimensions than other waveguide sections and,likewise, the waveguide gaps may be non-uniform. Similarly, althoughwaveguide sections and gaps are shown having generally rectilinear facesand profiles, alternative profiles may have curved or roundedcomponents.

FIG. 9D shows an alternative waveguide 150D having a generally roundbase suitable for use in combination with a generally round ultrasoundtransducer and a bullet-shaped body 152D with minor protuberances 154Dto promote fluid flow. Protuberances 154D are arranged in a generallyradially symmetrical arrangement around the circumference ofbullet-shaped body 152D and are arranged along a curved path. Theprotuberances taper from a narrower width at the smaller diameterportion of the bullet-shaped body to a larger width at the largerdiameter portion of the bullet-shaped body. Although three protuberancesare illustrated, it will be appreciated that a greater number ofprotuberances may be provides in a generally radially symmetricalarrangement.

FIG. 9E shows an alternative waveguide 150E having tapered side wallsand a converging portion 152E having a curved, generally centrallylocated apex 154E formed on the distal face. It will be appreciatedthat, although a simple, centrally placed curved apex 154E is shown, itmay be desirable in some circumstances to provide a more complex curvedapex or curved distal faces having other symmetrical or asymmetricalconfigurations.

FIG. 9F shows an alternative waveguide 150F that is conically shaped.FIG. 9G shows an alternative waveguide 150G that is biconical. FIG. 9Hshows an alternative waveguide 150H having a plurality of pyramid-shapedportions 152H. Certain design considerations regarding selection of anappropriate waveguide geometry will now be discussed. The shape of thewaveguides may be selected, for example, to achieve a particularcompression and/or focusing of the acoustic waves.

Within certain embodiments of the present invention, acoustic waveguidesare capable of acoustic coherent focusing of the ultrasonic wavestransmitted from the ultrasonic transducer. Acoustic coherent focusingmay be achieved, for example, by curving the waveguide tip wherein thetip comprises a conductive medium having a known sound speed.Alternatively, a section of ultrasound-conducting polymer having a knownwave speed may be added to the end of a curved waveguide to nearlycomplete focusing before entering a medium of variable sound speed(e.g., dispersive bubbly medium). Within such embodiments, a singlecurve may be employed to achieve a single focus, whereas a scallopedcurve is useful for producing multiple foci.

Within alternative embodiments, acoustic waveguides are capable ofacoustic incoherent focusing of the ultrasonic waves transmitted fromthe ultrasonic transducer. Acoustic incoherent focusing may be achieved,for example, by conical or wedge shapes that conduct sound into aprogressively smaller area in a semicoherent manner such that intensityincreases. Alternatively, multiple conical tips may be employed toprovide multiple areas of higher acoustic intensity.

Suitable acoustic waveguides may also adopt a propeller-like geometrysuch as a standard propeller design or a spiral design. Alternatively,an acoustic waveguide may have a hinged hydrofoil-like shape wherein itsmotion creates fluid lift and consequent fluid flow. The acousticwaveguide may have a generally smooth exterior surface, or the exteriorsurface may be rough or irregular. In some embodiments, the acousticwaveguide may be designed and fabricated to promote removal of plaque bydirect contact of portions of the acoustic waveguide with teeth. Contactof the waveguide with tooth surfaces may be provided by altering thethree-dimensional surface of the waveguide, such as by providingprotrusions on waveguide surfaces, or by mounting or embeddingprotrusions, such as fibers and the like, on waveguide surfaces.Acoustic waveguides of the present invention may include, for example,embedded bristle filaments, squeegee-shaped protrusions, molded orshaped protrusions similar to bristles, fibers, or the like. Theprotrusions or attached fibers may be arranged in an ordered pattern, orthey may be randomly arranged. In alternative embodiments, the waveguidesurface may be provided with regularly or irregularly spaceddepressions. These features may additionally or alternatively ensurethat a specified separation distance is maintained between the toothsurface and the bulk surface of the acoustic waveguide. This feature mayfind application in those applications wherein it is desired to minimizedirect transmission of ultrasound into the tooth structure and/or ifbubble activation occurs at a distance from the end of the acousticwaveguide and a spacing device is needed to maintain this distance.

Regardless of the precise material and/or geometry, acoustic waveguidesof the present invention are fabricated to generate fluid flow whenmoved on a toothbrush head. The desired fluid motion and transmission ofultrasound into the dental fluid may be achieved, for example, byemploying a flexible mechanical protrusion that extends into the dentalfluid. In such cases, motion of the acoustic waveguide may beside-to-side or oscillatory or rotational.

When acoustic waveguide motion is rotational, the motion may begenerally about or parallel to a longitudinal axis of the waveguide andmay be achieved with a wedge or cone, multiple wedges or cones in crossor star patterns, a pinwheel, and/or multiple wedges in a star patternwithout a center. Alternatively, rotational motion may be about the axisalong the toothbrush head, as may be achieved with a wedge- orrectangular-shaped acoustic waveguide.

Acoustic waveguides can also be designed to increase the intensity ofacoustic energy delivered to the surface of the teeth and gums. Forexample, an acoustic waveguide can be designed to contain and compressthe propagating acoustic energy into a smaller physical area. If thewaveguide is designed with materials of low acoustic attenuation andwith appropriate sound speed, the quantity of energy delivered from theend of the waveguide will be comparable to that transmitted into thewaveguide, but can be compressed into a smaller area and will thereforehave a higher energy density and/or acoustic intensity. Waveguide tipmotion creates an “acoustic painting” effect to broadly distributeacoustic energy.

In addition to low attenuation, waveguides are generally designed tochannel the acoustic energy along the waveguide, and transmit or “leak”a minimum of acoustic energy into the surrounding medium before it haspropagated to the end of the waveguide. One method for achieving this isto use a material having a sound speed substantially lower than thesurrounding fluid and having shallow slopes on the sides of thewaveguide (e.g., wedge shaped). The shallow slope of the waveguide wallscauses the propagating waves to contact the waveguide and fluidinterface at low grazing angles. Because the wavelength in the waveguideis shorter than that of the surrounding medium, the waves will onlycouple into less efficient subharmonic modes where the launch angle isdefined by the ratio of multiples of waveguide wavelengths tosurrounding media wavelengths. These poorly coupled modes oftransmission into the fluid do not extract large amounts of energy fromthe waveguide.

The combination of containing, transmitting, and compressing acousticenergy enables the generation of high intensity acoustic fields at thewaveguide tip and improves the efficiency of acoustic energy delivery.Therefore, lower electrical power levels are required to generateappropriate acoustic intensities for bubble activation. FIGS. 2A-2D (fora rectangular waveguide 124), FIGS. 3A-3F (for a wedge-shaped waveguide124X), and FIGS. 4A-4D (for a wedge-shaped waveguide having a curved end124Y) show finite element model and simulation results illustratingwaveguides designed to compress the acoustic field. FIG. 2A shows ageneral, simplified model of a toothbrush head 120 according to thepresent invention, as discussed in detail above. FIG. 2B shows thecorresponding portions of the finite element model used to model thetoothbrush head 120, including a stem 121′, an ultrasonic transducer122′, an impedance matching layer 129′, and a waveguide 124′. Plotsshowing the wave field soon after transmission showing propagation inthe waveguide are shown in FIGS. 2C, 3C, 3E, and 4C for selectedwaveguides. These figures evidence a low level of leakage into thesurrounding fluid. FIGS. 2D, 3D, 3F, and 4D show a wave field plotlater, after transmission, at which time the ultrasonic wave front iscompressed into the tip of the waveguide and the transmission into fluidemulsion is primarily from the waveguide tip.

In addition to increasing the acoustic intensity delivered bycompressing the acoustic field, the waveguide can be designed tocoherently focus energy into surrounding media beyond the tip of thewaveguide. This is accomplished by shaping the end of the acousticwaveguide to create an acoustic lens effect that will focus the wavesfrom the waveguide into a higher intensity field beyond the waveguide.This focusing effect can be achieved with one or multiple waveguidematerials combined together and shaped to create a focused field. Forinstance, a low attenuation, higher sound speed material may be used atthe end of the waveguide to continue propagating and focusing the wavefront before the wave front emerges into the higher attenuationtoothpaste emulsion. As with the acoustic field compression describedabove, the increased acoustic intensity achieved with the focusingeffect improves the device efficiency. Therefore, size, weight, power,and costs are reduced and battery life is extended for a final device.

Still further embodiments provide that the acoustic waveguide may beconfigured to exhibit improved fluid propulsion properties when used ina power toothbrush head in combination with a sonic component eitherwith or without an ultrasonic component.

The waveguide may be positioned having its longest dimension generallyaligned with the longitudinal axis of the toothbrush head, as shown inFIG. 2A, and the waveguide may be configured to approximate the contourof tooth surfaces throughout the mouth, the location of which is noteasily perceived by the user and conversely the location of which is notrequired to be known by the user for effective cleaning. Such anorientation is generally less dependent on user brushing technique/styleand allows the user to brush as he/she would without concern about thewaveguide location.

Alternatively, the waveguide may be positioned with its longestdimension generally transverse to longitudinal axis of the toothbrushhead, which allows the waveguide to drop into the interproximal spaceand provide tactile feedback to the user such that the user may indexmovement from one interproximal space to the next, thus providingcleaning induced by the ultrasound interproximally—where it is neededmost beyond the bristles. In this orientation, the waveguide may rely onthe natural tendency of fluid to fill the interproximal space in theoral cavity due to wetting of adjacent surfaces and wicking of fluid.Such an orientation may be less reliant on the brush head to carry thefluid and position it at the tip of the waveguide. Rather, it takesadvantage of the waveguide's penetration of the interproximal space andactivation of bubbles in the fluid naturally found in that location. Inanother embodiment, the acoustic waveguide may be oriented obliquelywith respect to the longitudinal axis of the brush head. The waveguidemay be positioned at the end of the brush head such that it can beeffectively used either on the facial or lingual surface, as well as onthe posterior surfaces of the molar teeth.

In addition to the functions performed by the acoustic waveguide asdescribed above, the waveguide, regardless of orientation, mayadditionally function to: (a) act as a standoff to prevent the user fromusing too much force when applying the bristles against the teeth,thereby reducing the incidence of gingival damage from excessive forceduring brushing; (b) act as a scrubbing agent, thus cleansing the toothsurface, and as such may contain a surface texture to enhance; (c) actas a gum massaging agent, thus stimulating the gums (as oftenrecommended by the dental professional) to reduce swelling and to helpcontour the tissue; (d) act as an agent to stimulate saliva flow,particularly of interest to individuals with xerostomia.

The Sonic Component

Within certain embodiments, toothbrushes of the present inventioncomprise a sonic component 16 (see, FIG. 1A) in combination with theacoustic waveguide 24 and/or ultrasonic transducer 22, described above.Typically, a sonic component 16 comprises a motor assembly thatgenerates sonic vibrations that are transmitted to the toothbrush head,thereby causing vibration of the acoustic waveguide 24 and/or bristletufts 26. Such sonic vibrations generate bubbly flow within the dentalfluid. For example, by employing a sonic component 16, the acousticwaveguide 24 can be made to lift and push dental fluid towards the teethas well as interproximal and subgingival spaces, with an associatedfluid flow of sufficient pressure and shear force to cause the erosionof plaque. A vibrating acoustic waveguide 24 of the present invention iscapable of moving fluid, including bubbly fluid, with sufficientvelocity and focus to achieve plaque removal from teeth severalmillimeters beyond the bristles 26 of the toothbrush head 20. Motorassemblies that may be suitably employed in the toothbrushes of thepresent invention are well known and readily available to those of skillin the art, and are exemplified by the toothbrush head drive mechanismspresented within U.S. Pat. No. 5,987,681, Pat. No. 6,421,865, Pat. No.6,421,866, Pat. No. RE 36,669, and U.S. Patent Publication Nos.2002/0095734, No. 2002/0116775, No. 2002/0124333, and No. 2003/0079304.Each of these U.S. Patents and Patent Applications is herebyincorporated by reference in their entireties.

Toothbrushes of the present invention are capable of generating fluidflows at a range of about 1 cm/sec to about 50 cm/sec at a distance ofbetween about 1 mm and 10 mm beyond the toothbrush bristle tips and/oracoustic waveguide. More typically, toothbrushes of the presentinvention are capable of generating fluid flows at a range of about 2cm/sec to about 30 cm/sec at a distance of between about 1 mm and 10 mmbeyond the toothbrush bristle tips and/or acoustic waveguide.Exemplified herein are toothbrushes that are capable of generating fluidflows of about 10 cm/sec at a distance of between about 1 mm and 10 mmbeyond the toothbrush bristle tips and/or acoustic waveguide.

It will be recognized by those skilled in the art that the generation ofbubbly flow by the sonic actions on the acoustic waveguide 24 does notrequire the ultrasonic component 16 described above. It is, however, thecombination of the ultrasonic transducer 22, acoustic waveguide 24, andsonic component 16 that together comprise a toothbrush head 20 in eitherremovable or fixed combination, with a handle 15 to achieve a preferredpower toothbrush embodiment of the present invention. It is thiscombination of sonic and ultrasonic components that yields the mostsurprising benefits of improved microscopic bubbly flow properties incombination with enhanced cavitation and acoustic microstreaning. Thesephysical properties provide superior cleaning properties of thisembodiment of the present invention. That is, the ultrasonic and soniccomponents, when used in combination to achieve toothbrush designsdisclosed herein, yield synergistic cleaning effects that aresubstantially superior to the additive effects of the sonic andultrasonic components in isolation. For example, the acoustic waveguide24 can be optimized to move bubbly fluid whose bubbles could facilitateacoustic streaming (thereby further enhancing the fluid flow generatedby the waveguide alone) as well as acoustic microstreaming andcavitation.

The primary function of the sonic motion is to activate the bristle tipssuch that they cleanse the tooth surface via direct bristle contact.This motion also relates to the user's primary perception of cleaningduring a typical brushing event. In the implementation of the combinedeffect of sonic and ultrasonic cleaning, sonic bristle motion is alsoused to generate bubbles within the dental fluid surrounding thewaveguide. Furthermore, the sonic motion propels dental slurry(including the fluid and the bubbles) towards the surface of the teeth.This fluid motion towards the teeth both acts to clean the teeth bydislodging plaque bacteria and debris as well as propel the bubbles tothe tooth surface where they can be acted upon by the ultrasound. Thisbulk fluid motion—itself enhanced by an optimally configured waveguide,with or without ultrasound transmission—can also carry maximallyoxygenated dental fluid into the gingival and sub-gingival region, witha therapeutic effect resulting from the reduction of anaerobic plaqueand other bacteria that reside in those regions.

The gaseous substance within bubbles in a dental fluid is typically airfound within the oral cavity during brushing. Movement of the bristles,waveguide, and/or other brush head components through the air/fluidinterface (fluid may be saliva, water, dentifrice, mouthwash and/orother present during typical brushing) acts to fracture this interfaceentrapping bubbles within the fluid. With respect to cleaning the toothsurface with shear induced by cavitation and/or acoustic streaming, thepositive benefits of ultrasound are achieved when bubbles within thefluid are stimulated to create cavitation and/or streaming. It isdesirable to use the sonic component of the toothbrush to generate thesebubbles within the dental slurry.

The dental slurry acts as both the source of the bubbles to be activatedby the ultrasound and as an ultrasound coupling media (transfer ofultrasound from waveguide tip to the tooth surface, which may be a gapfrom 0 to 10 mm, more typically 1 to 5 mm). If there is insufficientbristle and/or waveguide motion, too few bubbles are created within thedental slurry and the cleaning effect of the ultrasound on the toothsurface is reduced. If there are too many bubbles created in the dentalfluid, the fraction of air within the coupling media is too large,preventing the passage of ultrasound from the waveguide tip to the toothsurface and reducing the cleaning effect on the tooth surface.

Dentifrice Design and Compositions

Within certain related embodiments, it is contemplated to provide adentifrice that is particularly suitable for use with the inventivepower toothbrush described herein. For example, it is hereincontemplated that such a dentifrice will facilitate the creation of adesirable bubble population that may be acted upon by the ultrasonictransducer 22 and acoustic waveguide 24 disclosed herein.

The natural bubble population within a dental fluid can be assayed bythe tendency of that fluid to absorb ultrasonic energy that istransmitted through it. The higher the absorption, the more bubbles thatare present at the relevant size (given heuristically by the resonanceformula, developed originally for bubbles in pure water at 37 degreesCelsius, although applicable as an approximation for more generalconditions F₀R₀=3.26, where the frequency F₀ is given in MHz and theradius R₀ of the bubble is given in microns), although many bubblesoff-resonance would also create desired plaque and stain removaleffects.

A typical composition of dental slurry is 17% dentifrice in fluid. Thefluid may be, in part, water added to the toothbrush prior to brushing,but, more typically, the fluid is largely saliva generated by the userduring brushing. Components within the dentifrice (e.g., detergents,humectants, thickeners, etc.) influence the formation of bubbles withinthe dental slurry. Dentifrices according to the present inventionfacilitate the formation of bubbles having a diameter of between about 1μm and about 150 μm within the dental fluid that resonate whenultrasound is applied in the 20 kHz to 3 MHz frequency range. Moretypically, dentifrices according to the present invention facilitate theformation of bubbles having a diameter of between about 1 μm and about100 μm within the dental fluid that resonate when ultrasound is appliedin the 30 kHz to 3 MHz frequency range. Still more typically,dentifrices according to the present invention facilitate the formationof bubbles having a diameter of between about 5 μm and about 30 μmwithin the dental fluid that resonate when ultrasound is applied in the100 kHz to 600 kHz frequency range. In an exemplary dentifrice presentedherein, bubbles that have a diameter of between about 12 μm and about 26μm are formed in the dental fluid and resonate when ultrasound isapplied to those bubbles with an ultrasound transducer operating in the250 kHz to 500 kHz range.

Dentifrices suitable for use with the toothbrushes disclosed hereincomprise a surfactant that produces surface tension values thatfacilitate production and stabilization of bubbles in a suitable sizerange for stimulation by the ultrasonic transducer in combination withan acoustic waveguide. Typically, surfactants employed in thedentifrices disclosed herein produce surface tensions in the range ofabout 0.1 Pa to about 500 Pa, more typically in the range of about 0.2Pa to 250 Pa, and still more typically in the range of about 0.5 Pa toabout 50 Pa.

Alternatively, or in addition to providing a dentifrice as describedabove that promotes bubble formation, bubbles having a desired sizerange may be incorporated in a dentifrice or another composition andintroduced directly into the oral cavity by application of thecomposition on a toothbrush or by introduction of the composition intothe oral cavity. Bubbles having a diameter of between about 1 μm andabout 150 μm, more typically between about 1 μm and about 100 μm, insome embodiments between about 5 μm and about 30 μm, and in yet otherembodiments between about 12 μm and about 26 μm may be incorporateddirectly in a dentifrice composition or in another composition, such asa mouthwash or another generally liquid, gel-like or semi-solid carrierfor delivery to the oral cavity.

Bubbles in the carrier material may be present as voids in thecomposition itself, or as microspheres or other microstructures forminggas-filled voids in the carrier material. The OPTISON™ ultrasoundcontrast enhancing composition, for example, comprises a suspension ofmicrospheres having a mean diameter of 2.0-4.5 μm, the microspheresbeing formed from human serum albumin and being filled with anoctafluoropropane gas. A population of microspheres of the desired sizerange (as described above), formed using a material that's safe forhuman consumption and generally inert, and filled with a gas that's safefor human consumption and generally inert may be incorporated in asuitable carrier material and used, in conjunction with toothbrushes ofthe present invention, to promote effective cleaning.

The following examples are provided to exemplify, but not to limit, thepresently disclosed invention.

EXAMPLES Example 1 Design and Construction of a Combined Sonic andUltrasonic Toothbrush

Prototype power toothbrushes were generated by replacing internalbristle tufts of commercially available power toothbrushes with anultrasonic transducer and acoustic waveguide. Ultrasonic transducersemployed in these prototype toothbrushes had significant power outputwithin the frequency range of about 150 to about 510 (generally 500) kHzthat was sufficient to stimulate the formation of an acousticallysignificant bubble population susceptible to resonant stimulation byenergy emitted by the ultrasonic transducer. A polymer waveguide wasmolded onto the toothbrush head in operable proximity to the ultrasonictransducer and positioned such that ultrasonic waves generated by theultrasonic transducer were propagated and focused.

Several acoustic waveguides were used experimentally and were locatedgenerally in the center of and along the longitudinal axis of thebrushhead. The most common dimensions were: length=11.4 mm; width=3.1mm; maximum height at the center of a curved end face=7.4 mm; height atthe edges of a curved end face=4.3 mm. The ultrasound operatingparameters generally used experimentally were: 250 kHz frequency; 1-10%duty cycle; 10-1,000 cycles/second and PRF=1-500.

Example 2 Ultrasonic Imaging and Plaque Removal by an ExemplaryUltrasonic Power Toothbrush

This example discloses ultrasound imaging and plaque removal datacollected for one of the prototype power toothbrushes described inExample 1.

In order to demonstrate the improved performance of a power toothbrushemploying an ultrasonic transducer in combination with an acousticwaveguide, Doppler, and B-mode data were collected for a prototypeultrasonic toothbrush with and without incorporating an acousticwaveguide. FIG. 5A presents an ultrasound image of an ultrasonictoothbrush without an acoustic waveguide. Doppler data show fluid flow(within box) and B-mode data highlight acoustic backscatter (outside ofbox) at the bristle tips (BT) and bristle plate (BP) at bottom ofbristles. FIG. 5B presents the same ultrasonic toothbrush with movingbristles powered by a sonic component. These data reveal that fluid flow(FF) beyond the bristle tips is not detectable even though the bristlesare moving (MB). FIG. 5C presents an ultrasound B-mode image of aprototype ultrasonic toothbrush in combination with an acousticwaveguide. The sonic component drives the vibration of the acousticwaveguide and generates a jet of bubbly fluid moving away from thebrush. FIG. 5D presents Doppler and B-mode ultrasound image data of thesame toothbrush showing significant fluid flow (FF) and bubbles (B)beyond the bristles.

A prototype ultrasonic power toothbrush was tested for plaque removal ina plaque coated (Streptococcus mutans) artificial tooth model system.Plaque was detected by staining a set of artificial teeth beforeapplication of fluid flow generated by an acoustic waveguide, withoutultrasound, positioned several millimeters beyond the toothbrush headbristle tips. Discrete plaque colonies were reduced or removed afterapplication of fluid flow generated by the ultrasonic transducer incombination with the acoustic waveguide.

An artificial tooth model for tooth areas outside the reach of atoothbrush head bristle tip was also tested. Plaque was dyed pink beforeapplication of ultrasonic energy from several millimeters beyond thebristle tips. Discrete plaque colonies were reduced or removed afterapplication of ultrasound. Background films of plaque were also reduced,leaving residual pink due primarily to dye that has leached into theteeth. Plaque removal in the same model system was also tested afterapplication of fluid flow generated by an acoustic waveguide and afterapplication of ultrasonic energy from several millimeters beyond thebristles. Discrete plaque colonies were reduced or removed aftertreatment. Background films of plaque were also reduced, leavingresidual pink due primarily to dye that has leached into the teeth.Superior results were achieved while simultaneously using microscopicfluid flow from the acoustic waveguide and ultrasound.

Example 3

Measurement of Physical Parameters of an Exemplary Ultrasonic PowerToothbrush Employing an Acoustic Waveguide

This example discloses measurements of physical parameters of anexemplary ultrasonic power toothbrush of the present invention.

In order to compare the effectiveness of various acoustic waveguidegeometries, the transmitting pressures for a flat, unfocusedelastomeric/silicone polymer wedge waveguide (FIG. 3) was compared tothe transmitting pressures for a focused elastomeric/silicone polymerwedge waveguide (FIG. 4). The plot of acoustic pressure levels at thetip of each acoustic waveguide presented in FIG. 6 demonstrates anapproximately three-fold increase in transmitting pressure for a focusedwaveguide (˜1.5 MPa tip pressure) versus an unfocused waveguide (˜0.5MPa tip pressure).

The absorption of ultrasound transmitted through a model dentalfluid/bubble emulsion was measured as a function of ultrasonic frequencyin the 30 to 700 kHz frequency range. Ultrasonic transducers werepositioned, approximately 0.3 to 1 cm apart, on opposite sides of aPetri dish containing simulated dental fluid (i.e., an emulsification ofdentifrice and water) and the intensity of sound transmitted through thefluid was measured and normalized by the intensity of sound transmittedinto the fluid. Results of an exemplary test are presented in FIG. 7,which reveals a peak in attenuation due to absorption of sound atapproximately 200 kHz and a spurious dip in the curve at approximately350 kHz, owing to resonance between the length of the ultrasound waveand the depth of the fluid. These data demonstrated the presence of asignificant bubble population available for acoustic stimulation atfrequencies between 100-500 kHz.

Example 4 Plague Removal by an Exemplary Ultrasonic Power Toothbrush

This example discloses plaque removal with the bubbly jet generated bythe sonic vibration of an acoustic waveguide in combination withultrasound stimulation of the bubbles within the jet.

A Streptococcus mutans model for dental plaque was employed to assessplaque removal by an exemplary ultrasonic toothbrush of the presentinvention. S. mutans (human-derived plaque) was allowed to grow onfrosted glass slides, then exposed to a prototype toothbrush operated atthe surface of a water bath and held a few millimeters away from, in aperpendicular fashion, the surface of the slide. A variety of ultrasoundprotocols were used, including waveguide only (WG) and waveguide plusultrasound (WG/US). The slides were stained with a plaque-specific dyeto indicate intact plaque (pink) and plaque-free regions (white).

In an exemplary assay, the surface of an S. mutans-coated slide wasplaced 4 mm from the longest bristles of a prototype toothbrush. Theultrasound carrier frequency was 250 kHz, with a PRF of 1000 Hz and with24 cycles per burst; the Mechanical Index was 0.75. With only the bubblyfluid jet produced by the acoustic waveguide, there was a subtlereduction in the thickness of the plaque, while in concert withultrasound, significant plaque was removed. For comparison, acommercially available power toothbrush was held at the same distancefrom plaque grown on the frosted glass slide. That control toothbrushdid not remove meaningful plaque.

A second assay system used hydroxyapatite (HA) disks incubated for 48hours prior to the experiment with S. Mutans. The ultrasound protocolconsisted of a 250 kHz run at 625 Hz PRF, 40 cycles/sec, 3 secondexposure, and a Mechanical Index of 0.9 measured at 6 mm from the tip ofthe acoustic waveguide.

The action of the acoustic waveguide alone removed some plaque; however,in combination with ultrasound, there was significantly improved plaqueremoval. By comparison, a commercially available power toothbrush didnot remove any plaque, while ultrasound alone removed only a few spotsof plaque, in a small region of the disk.

In a third experimental system, an ultrasound protocol was followed thatconsisted of a 510 kHz run at 1,252 Hz PRF, with 2 cycles/sec, exposedfor 3 seconds, with a Mechanical Index of 0.51 measured at 6 mm from thetip of the waveguide. Consistent with the assays described above, theaction of the acoustic waveguide alone removed some plaque; but, incombination with ultrasound, there was significantly improved plaqueremoval. By comparison, a commercially available power toothbrush, held1-2 mm away from the front of the teeth, removed only some plaque, whileultrasound alone only removed a few spots of plaque in a small region ofthe disk. Thus, the bubbly fluid jet generated by the sonicallyvibrating acoustic waveguide was sufficient to achieve more rapid plaqueremoval beyond the reach of the bristles by a factor of at leasttwo-fold greater than the commercial power toothbrush.

Plaque removal was observed across a wide range of acoustic protocols.Optimal plaque removal was achieved when the PRF was a multiple, greaterthan one, of the sonic frequency. Without wishing to be bound to anyspecific theory of operation, it is believed that this protocol resultedin optimal plaque removal because it allowed multiple pulses ofultrasound to interact with the bubbly jet and the plaque as theflexible tip of the acoustic waveguide was being oscillated back andforth across the face of the HA disk, relevant portion of the glassslides, and/or the teeth. It is further believed that this accounts, atleast in part, to the synergistic effect observed with the combinedaction of a bubbly fluid jet and ultrasound.

In order to demonstrate this synergistic effect, the action ofultrasound alone on a tooth/model of plaque removal was assessed bothwith and without motion of the acoustic waveguide. An ultrasoundprotocol was chosen that, by itself, did not yield meaningful plaqueremoval (with or without the production of a bubbly jet), but did soafter introduction of dental fluid containing artificial bubbles(Optison™). The results of this study also demonstrated that ultrasoundalone was not responsible for plaque removal; but, rather, it was theultrasound stimulation of the artificial bubbles that, in combination,yielded substantial plaque removal.

Additional studies performed in an artificial tooth dental plaque modelfor tooth areas beyond the reach of the toothbrush's bristlesdemonstrated that a sonically vibrating acoustic waveguidesimultaneously emitting ultrasound at 450 kHz in the presence ofartificial bubbles removed plaque from a distance of 2-3 mm after only 5seconds of application, although that plaque removal pattern actuallyappeared within a fraction of a second of ultrasound onset. This plaqueremoval occurred over a larger area than with ultrasound alone andoccurred in an appreciably shorter length of time than that created bythe bubbly fluid jet alone. Therefore, the ultrasound and sonicallygenerated bubbly fluid flow acted together in a synergistic fashion torapidly and effectively remove plaque over a large area, beyond thereach of the bristles.

Because a bubble's volume oscillates and associated stresses act on atime scale governed by the ultrasound frequency, the frequencies (on theorder of 100s of kHz), plaque removal can, in principle, occur on timescales on the order of 0.00001 seconds (i.e., approximately 10microseconds). Therefore, ultrasound toothbrushes of the presentinvention are capable of substantial plaque removal at times that areapproximately 100- to 1000-fold shorter than the time required forplaque removal by existing power toothbrushes.

Example 5 Absence of Cell Lysis by an Exemplary Ultrasonic PowerToothbrush

This example discloses that ultrasonic power toothbrushes of the presentinvention induces ultrasonic cavitation whose mechanical effects wereinsufficient to induce cell lysis, yet were able to remove plaque. Thesefindings support the safety of ultrasonic power toothbrushes providedherein.

A red blood cell model system was utilized (FIG. 8) to test cell lysiscaused by shear stresses induced by acoustic microstreaming associatedwith stable oscillating bubbles by Rooney, Science 169:869-871 (1970),who demonstrated that a single bubble, placed within a vial of dilutered blood cells, could be stimulated by ultrasound to produce“microstreaming” such that with sufficient acoustic power, those bloodcells could be disrupted. In particular, a thin, hollow wire with air inits center was placed in a vial of suspended red blood cells. Sufficientair was extruded from the wire to form a hemisphere of gas (themicrobubble) within the suspension. Ultrasonic waves at a frequency ofabout 25 kHz were applied to the container to stimulate oscillation ofthe bubbles and sufficient to generate acoustic microstreaming. Underthese conditions, about 70% of the red blood cells were destroyed atshear stresses comparable to those determined via independent means. Onehundred percent hemolysis was achieved by introduction of a highlyosmotic solution. Of particular interest here is the difference in shearstress (greater than 450 Pa) necessary to break up the cells, versusstress necessary to remove fresh plaque in vitro (1-30 Pa). The shearrequired for detachment of P. aeruginosa biofilms grown at shearstresses of 0.075 and 5.09 Pa were 5.09 Pa and 25.3 Pa, respectively.Stoodley et al., Journal of Industrial Microbiology & Biotechnology29:361-367 (2002).

Acoustic microstreaming, just one of a variety of physical processesassociated with acoustic cavitation (the formation and/or stimulation ofbubbles by acoustic energy), can cause disruption of biological systemssuch as red blood cells, as discussed herein. Of particular interest isthat the presence of bubbles can facilitate stresses sufficient toremove plaque, for example, at acoustic intensities far below thatnecessary to cause desired biological effects, when no bubbles arepresent. In the present example, Optison™, a microbubble ultrasound (US)contrast agent with a diameter of about one micron, was used todemonstrate this point. This example also shows that it is theultrasound stimulation of bubbles, not ultrasound cavitation alone, thatremoves plaque.

As evidence for the safety of ultrasonic toothbrushes of the presentinvention, the following plaque removal assay system was employed. Celldisruption by an exemplary toothbrush was determined by assaying celldebris in the liquid above plated gingival cells that were exposed to(1) an activated commercial power toothbrush whose bristle tips wereplaced above the cells, (2) a bubbly fluid jet caused by the soniccomponent of the prototype toothbrush held above the cells, and (3) thecombination of bubbly fluid jet and ultrasound (sonic plus ultrasound)from the prototype toothbrush, held above the cells. These results werecompared to the results achieved with a commercial power toothbrushwhose bristle tips were placed directly on the cells.

Following treatment, supernatants were evaluated for lysed cells by anonradioactive lactate dehydrogenase (LDH) assay (Cytotox 96; Promega,Madison, Wis.) according to the manufacturer's instructions. This assaysystem is a calorimetric alternative to ⁵¹Cr release cytotoxicity assaysand has been used to measure cell lysis by chemical and physical means.Singer et al., J. Neurosci. 19:2455-2463 (1999). The assayquantitatively measures LDH, a stable cytosolic enzyme that is releasedupon cell lysis in much the same way as ⁵¹Cr is released in radioactiveassays. Released LDH in culture supernatants is measured with a30-minute coupled enzymatic assay, which results in the conversion of atetrazolium salt (INT) into a red formazan product. The amount of colorformed is proportional to the number of lysed cells.

Visible wavelength absorbance data were collected using a standard 96well plate reader. Methods for determination of LDH utilizingtetrazolium salts in conjunction with diaphorase or alternate electronacceptors are well known in the art. Variations on this technology havebeen reported for measuring natural cytotoxicity and have beendemonstrated to be identical (within experimental error) to valuesdetermined in parallel ⁵¹Cr release assays.

Cells remaining in plates following treatment were photographed, lysed,and quantified using the LDH assay as described above. Cell lysisinduced by the beyond the bristle effects of a sonic toothbrush wascompared to cell lysis induced by a prototype combined sonic/ultrasonictoothbrush of the present invention.

Results of an exemplary assay are presented in FIG. 10, whichdemonstrate that the cleaning action of a bubbly fluid jet generated byan acoustic waveguide mounted on a toothbrush, in combination withultrasound propagated through the acoustic waveguide, safely removedplaque. The “control” result was a measure of cell lysis caused by thefluid action generated beyond the reach of the bristles of a commercialpower toothbrush; the “sonic” result was a measure of such cell lysis byan exemplary toothbrush without ultrasound; the “sonic+ultrasonic”result was a measure of such cell lysis by an exemplary toothbrush withboth a sonic component and ultrasound; and the “control+contact” resultwas a measure of cell lysis by a commercial power toothbrush whosebristles were placed in direct contact with the cell surface. There wereno differences detected between the commercial toothbrush and theprototypical toothbrush when their bristles did not touch the cells. Incontrast, there was substantial cell lysis generated by the directcontact of the toothbrush bristles of a commercial power toothbrush uponthe cells.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

1. A toothbrush comprising: a toothbrush head including an acousticwaveguide and a plurality of bristle tufts projecting from a toothbrushhead support structure, wherein the acoustic waveguide comprises apolymer having a durometer hardness less than 100 Shore A; and anultrasonic transducer acoustically coupled to the acoustic waveguide,wherein the ultrasonic transducer is adapted to oscillate at ultrasonicfrequencies.
 2. The toothbrush of claim 1, wherein the polymer has adurometer hardness between about 10 and about 65 Shore A.
 3. Thetoothbrush of claim 1, wherein the polymer is silicone rubber.
 4. Thetoothbrush of claim 1, wherein the ultrasonic transducer is mounted inthe toothbrush head in proximity to the acoustic waveguide.
 5. Thetoothbrush of claim 1, wherein the acoustic waveguide comprises a basestructure mounted in the toothbrush head and a distal portion extendingoutwardly from the base structure.
 6. The toothbrush of claim 5, whereinthe base structure is larger cross-section than the distal portion. 7.The toothbrush of claim 1, wherein the acoustic waveguide issubstantially rectangular in profile.
 8. The toothbrush of claim 1,wherein the acoustic waveguide includes oppositely disposed side wallsthat are tapered and terminate distally in a waveguide face.
 9. Thetoothbrush of claim 1, further comprising an impedance matching layerdisposed between the ultrasonic transducer and the acoustic waveguide.10. The toothbrush of claim 1, wherein the ultrasonic transducercomprises a plurality of piezoelectric elements.
 11. The toothbrush ofclaim 10, wherein the plurality of piezoelectric elements aremechanically stacked and electrically connected in parallel.
 12. Thetoothbrush of claim 11, wherein the plurality of piezoelectric elementscomprise two piezoelectric elements.
 13. The toothbrush of claim 12,further comprising at least one electrical contact contacting each ofthe piezoelectric elements.
 14. The toothbrush of claim 1, wherein theultrasonic transducer operates at an ultrasound carrier frequency in therange of about 100 kHz to about 750 kHz.
 15. The toothbrush of claim 1,wherein the ultrasonic transducer operates at an ultrasound carrierfrequency of less than about 750 kHz.
 16. The toothbrush of claim 1,wherein the ultrasonic transducer operates at an ultrasound carrierfrequency of less than about 500 kHz.
 17. The toothbrush of claim 1,wherein during use the ultrasonic transducer oscillates periodicallywith a pulse repetition frequency of between about 0.5 Hz and about 225Hz.
 18. The toothbrush of claim 1, wherein the ultrasonic transduceroscillates periodically with a pulse repetition frequency of betweenabout 5 Hz and about 1,500 Hz.
 19. The toothbrush of claim 18, whereinthe ultrasonic transducer operates with a duty cycle between about 5%and about 15%.
 20. A toothbrush comprising: an ultrasonic transduceradapted to operate within the following ranges of operating parametersduring use: 100-750 kHz carrier frequency; 0.5-1500 Hz pulse repetitionfrequency (PRF); and 50-10,000 cycles/burst; a plurality of bristletufts projecting from a toothbrush head; and an acoustic waveguideacoustically coupled to the ultrasonic transducer and projecting fromthe toothbrush head.
 20. The toothbrush of claim 19, wherein theultrasonic transducer operates at a mechanical index of less than 1.9.21. The toothbrush of claim 19, wherein the ultrasonic transduceroperates at a duty cycle of less than about 15%.
 22. A toothbrush ofclaims 19 wherein the ultrasonic transducer operates at a pulserepetition frequency (PRF) of from about 40-200 Hz.
 23. A toothbrush ofclaim 19 wherein the ultrasonic transducer operates at a pulserepetition frequency (PRF) of less than about 20 Hz.
 24. A toothbrushcomprising: a toothbrush head having an acoustic waveguide and aplurality of bristle tufts, the acoustic waveguide having at least twoopposing faces terminating in a distal waveguide face; and a soniccomponent coupled to the toothbrush head to vibrate the acousticwaveguide and the bristle tufts at a sonic acoustic frequency.
 25. Thetoothbrush of claim 24, wherein the acoustic waveguide has tapered sidewalls forming generally a wedge-shaped waveguide, wherein a waveguidebase portion has a larger cross-sectional area than the distal waveguideface.
 26. The toothbrush of claim 24, wherein the distal waveguide faceis curved.
 27. The toothbrush of claim 24, wherein the distal waveguideface is generally convex.
 28. The toothbrush of claim 24, wherein theacoustic waveguide has a hardness of approximately 40 Shore A or less.29. The toothbrush of claim 24, wherein the acoustic waveguide isoriented generally parallel to a longitudinal axis of the toothbrushhead.
 30. The toothbrush claim 24, wherein the acoustic waveguide isoriented generally transverse to a longitudinal axis of the toothbrushhead.
 31. A toothbrush head comprising a support structure, an acousticwaveguide and a plurality of bristle tufts projecting from the supportstructure, the acoustic waveguide having multiple opposing faces, withat least two opposing faces having walls terminating in a distalwaveguide face; and an ultrasonic transducer acoustically coupled to theacoustic waveguide and capable of producing ultrasonic energy atfrequencies of less than about 1000 kHz.
 32. A toothbrush head formounting on a toothbrush handle, the toothbrush head comprising anacoustic waveguide, an ultrasonic transducer operably connected to theacoustic waveguide, and a plurality of bristle tufts projecting from atoothbrush head support structure, the acoustic waveguide having agenerally block-like structure and having an exposed height that isgreater than about 50% and less than about 120% of the exposed height ofthe bristle tufts.
 33. The toothbrush of claim 32, wherein the acousticwaveguide comprises a polymer having a durometer hardness between about10 and about 65 Shore A.
 34. The toothbrush of claim 33, wherein thepolymer is silicone rubber.
 35. The toothbrush of claim 32, furthercomprising an impedance matching layer disposed between the ultrasonictransducer and the acoustic waveguide.
 36. The toothbrush of claim 32,wherein the ultrasonic transducer comprises a plurality of piezoelectricelements.
 37. The toothbrush of claim 36, wherein the plurality ofpiezoelectric elements are mechanically stacked and electricallyconnected in parallel.
 38. The toothbrush of claim 37, wherein theplurality of piezoelectric elements comprise two piezoelectric elements.39. The toothbrush of claim 37, further comprising at least oneelectrical contact contacting each of the piezoelectric elements. 40.The toothbrush of claim 32, wherein the ultrasonic transducer operatesat an ultrasound carrier frequency in the range of about 100 kHz toabout 750 kHz.
 41. The toothbrush of claim 40, wherein the ultrasonictransducer oscillates periodically with a pulse repetition frequency ofbetween about 0.5 Hz and about 225 Hz.